Assessment of Central Sensitivity Syndrome and Sensory Processing Sensitivity: A Systematic Review.

Conceptualization : Mercedes Borda‐Mas and Gema Chamorro‐Moriana; Formal analysis : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, Nerea Almeda, Carmen Ridao‐Fernandez, and Magdalena Sánchez‐Fernández; Investigation : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, Nerea Almeda, Carmen Ridao‐Fernandez, and Magdalena Sánchez‐Fernández; Methodology : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, and Nerea Almeda; Supervision : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, and Magdalena Sánchez‐Fernández; Validation : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, Nerea Almeda, Carmen Ridao‐Fernandez, and Magdalena Sánchez‐Fernández; Visualization : Mercedes Borda‐Mas and Carmen Ridao‐Fernandez; Roles/writing – original draft : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, Nerea Almeda, Carmen Ridao‐Fernandez, and Magdalena Sánchez‐Fernández; Writing – review and editing : Mercedes Borda‐Mas, Gema Chamorro‐Moriana, Nerea Almeda, Carmen Ridao‐Fernandez, and Magdalena Sánchez‐Fernández.

A total of 1600 records were identified: 1587 from electronic databases and 13 through manual search (i.e., gray literature). After duplicate removal, studies were selected by title, abstract, and full text according to the inclusion criteria. Following the rejection of records that did not meet the criteria, 697 remained, of which 13 originated from gray literature. After this selection, 29 original validation studies, corresponding to the 29 tools included in the review, were retained. Note: This review additionally referenced 59 more studies (11 subsequent validations and 48 cross‐cultural adaptations), totaling 88 studies. Figure  2 presents a flowchart of the study selection process based on the PRISMA protocol [ 30 ]. PRISMA flowchart [ 30 ]. The 29 original validation studies used 29 assessment instruments. Sixteen tools (55.17%) were associated with CSS: Brief Environmental Exposure and Sensitivity Inventory (BREESI) [ 34 ], Complex Medical Symptom Inventory (CMSI) [ 35 ], Central Sensitization Inventory (CSI) [ 36 ], Central Sensitization Inventory Short Form (CSI‐9) [ 37 ], Environmental Hypersensitivity Symptom Inventory (EHSI) [ 38 ], Environmental Symptom‐attribution Scale (ESAS) [ 39 ], Fear‐Avoidance Components Scale (FACS) [ 40 ], Generalized Pain Questionnaire (GPQ) [ 41 ], Idiopathic Environmental Intolerance Symptom Inventory (IEISI) [ 42 ], Multisensory Amplification Scale (MSAS) [ 43 ], Quick Environmental Exposure and Sensitivity Inventory (QEESI) [ 44 ], Sensory and Behavioral Modulation Questionnaire (SENSE) [ 45 ], Sensory Sensitivity Scale (SHS) [ 46 ], Sensory Perception Quotient (SPQ) [ 47 ], Somatic Symptom Scale‐8 (SSS‐8) [ 48 ], and The Chemical Odor Intolerance Index (CII) [ 49 ]. The remaining 13 tools (44.83%) were related to SPS: Adult Sensory Profile (ASP) [ 50 ], Adult Sensory Questionnaire (ASQ) [ 51 , 52 ], DOES Scale [ 53 ], High Interpersonal Sensitivity Scale (HISS) [ 54 ], Highly Sensitive Person Scale (HSPS) [ 16 ], Highly Sensitive Child Scale (HSCS) [ 55 ], Highly Sensitive Child‐Rating System (HSCS‐RS) [ 56 ], Highly Sensitive Child Interview (HSCS‐I) [ 57 ], The Parent‐Report version of the Highly Sensitive Child Scale (HSCS‐PR) [ 58 ], Lynn and Accardi Sensitivity Scale (LASS) [ 59 ], Sensory Processing Sensitivity Questionnaire (SPSQ) [ 60 ], Sensory Processing Sensitivity Questionnaire Short Form (SPSQ‐26) [ 61 ], and Temperamental Sensitivity Q‐Scale (TSQ‐scale) [ 62 ]. The 29 original validation studies included 29,553 participants, of whom 2453 corresponded to families (at least one parent plus the child). The characteristics of the assessment instruments, original validation studies, and additional associated information are listed in Table  3 . Complementary data regarding subsequent validations and cross‐cultural adaptations by language associated with each identified tool were also provided. The 11 subsequent validations belonged to five scales, with CSI standing out due to the number of validations. It adds four complementary validations [ 21 , 63 , 64 , 65 ] to its original validation [ 36 ]. The ASQ had two subsequent validations [ 51 , 52 ], as did BREESI [ 66 , 67 ] and HSPS [ 29 , 68 ]. There is only one FACS [ 21 ]. Of the 48 cross‐cultural adaptations identified, those associated with CSI stood out again for their quantity: 20 [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 ]. These were followed by the 19 adaptations related to two specific tools for evaluating SPS: 13 from HSPS for adults [ 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ] and six from HSCS for children [ 102 , 103 , 104 , 105 , 106 , 107 ]. CSI‐9 had two cross‐cultural adaptations [ 108 , 109 ], as did FACS [ 75 , 110 ] and QEESI [ 111 , 112 ]. ASQ had one adaptation [ 113 ], similar to LASS [ 114 ] and SPSQ [ 115 ]. All tools were self‐administered, with the exception of two that depended on a clinician: HSCS‐I [ 57 ], an interview conducted with parents about their child's potential high sensitivity, and HSCS‐RS [ 56 ], an observational technique. Of the total instruments, 24 were originally validated with samples composed of adult populations (≥18 years), one considered early adolescents, HSCS [ 55 ], and four evaluated children through parents or educators: HSCS‐RS [ 56 ], HSCS‐I [ 57 ], HSCS‐PR [ 58 ], and TSQ‐Scale [ 62 ]. Regarding the availability of the identified tools: 11 were included entirely in the original validations (BREESI [ 34 ], CSI [ 36 ], DOES [ 53 ], EHSI [ 38 ], FACS [ 40 ], HSCS‐RS [ 56 ], IESI [ 42 ], LASS [ 59 ], QEESI [ 44 ], SENSE [ 45 ], and SSS‐8 [ 48 ]); 14 could be configured using the item statements, scores, and interpretations found in those validations (CSI‐9 [ 37 ], CMSI [ 35 ], ESAS [ 39 ], GPQ [ 41 ], HSPS [ 16 ], HSCS [ 55 ], HSCS‐I [ 57 ], MSAS [ 43 ], SHS [ 46 ], SPQ [ 47 ], SPSQ [ 60 ], SPSQ‐26 [ 61 ], CII [ 49 ], and TSQ‐S [ 62 ]); ASP [ 50 ] was located on a commercial website; HISS [ 54 ] was requested from the authors; ASQ [ 51 , 52 ] was configured through the analysis of its cross‐cultural adaptation; and HSCS‐PR [ 58 ] was formed by replacing the first‐person statements of the original HSCS items with “My child…” or “For my child…,” and so on. Regarding the application of QUADAS‐2, the risk of bias assessment showed varying levels of methodological quality across the domains (Table  4 ). The patient selection domain showed the weakest results, with 15 out of 29 studies (51.72%) showing a high risk of bias. The 14 remaining studies (48.26%) were evaluated as low risk [ 35 , 37 , 38 , 39 , 40 , 41 , 44 , 48 , 55 , 56 , 58 , 60 , 61 , 62 ]. In the index test domain, 26 out of 29 studies (89.66%) were rated as low risk, while three studies (10.34%) were rated as unclear [ 44 , 54 , 116 ]. The reference standard domain showed a moderate profile, where 20 out of 29 studies (68.97%) were rated as low risk, while nine studies (31.03%) were rated as unclear [ 39 , 41 , 46 , 49 , 57 , 59 , 60 , 116 ]. The flow and timing domains showed the highest proportion of favorable ratings, with all 29 studies (100%) presenting a low risk of bias. Therefore, procedures related to test execution and timing are considered well‐reported and at a low risk of bias, whereas patient selection strategies and use of reference standards domains showed a higher risk of bias. In regard with the concerns related to applicability, in the patient selection domain, 14 studies (48.28%) were rated as high concern. However, 13 studies (44.83%) were considered to be of low concern, while two studies (22.22%) were considered unclear [ 35 , 54 ]. The index test domain showed favorable results, with 89.66% of the studies classified as low concern and three as unclear (10.34%) [ 44 , 54 , 116 ]. The reference standard domain showed similar results, where 19 studies (65.52%) were rated as low concern, although 10 studies (34.48%) were marked as unclear [ 39 , 41 , 45 , 46 , 47 , 49 , 57 , 59 , 60 , 116 ]. Results related to the concerns on applicability showed that, overall, the studies included in the review presented strong applicability, especially with regard to the index tests. Nevertheless, concerns related to patient selection criteria and reporting information on the reference standard showed poor results. The assessment of methodological quality using COSMIN RB showed strong psychometric properties in most domains (Table  5 ). All studies included in the review (100%) were rated as “adequate” in the PROM development and content validity domains. The domain of structural validity showed slightly lower performance, where 27 out of 29 instruments were rated as “adequate,” and two studies (6.9%) were not evaluated [ 67 , 116 ]. The internal consistency domain showed that 27 studies (93.10%) were rated as “adequate,” while two studies (6.9%) did not assess this domain [ 67 , 116 ]. With respect to the construct validity test, 28 studies (96.55%) were considered as “adequate.” In contrast, the reliability domain showed greater variability; 10 studies (34.48%) achieved an “adequate” rating, while 15 studies (51.72%) were not assessed, and four studies (13.79%) were considered “doubtful” [ 46 , 47 , 49 , 59 ]. Concerning the results obtained in measurement error, 20 studies (68.97%) did not report this domain, six studies (20.69%) were rated as “doubtful,” and three studies (10.34%) were “adequate” [ 37 , 53 , 54 ]. The criterion validity domain was not assessed in nine studies (31.03%), while 18 studies (62.07%) were considered “adequate” and two studies were “doubtful” (6.9%) [ 55 , 59 ]. Lastly, the responsiveness domain was rated as “adequate” in one study (3.49%) [ 37 ] and “doubtful” in two studies (6.9%) [ 40 , 41 ], while the remaining 26 studies (89.66%) did not assess this domain. A detailed list of categories, grouped variables (subscales, components, factors, scales, domains, dimensions, sections [FACS] [ 40 ], reactions [HSCS‐I] [ 57 ], systems of multisensory sensitivity [MSAS] [ 43 ]), and specific variables of each assessment instrument are presented in Table  S1 . Figure  3 illustrates the number of grouped variables and tools associated with each category (absolute values and percentages), thus complementing Table  S1 . The variables and tools associated with each category are shown as absolute values and percentages. The Cronbach's alpha coefficients reflecting the internal consistency of the validation studies for the most representative scales were as follows: CSI 1 (original), 0.879; CSI 5, 0.93; HSPS 1—Study 6 (original), 0.87; HSPS 1—Study 7 (original), 0.85; HSPS 2, 0.89; HSPS 3, 0.89; FACS 1 (original), 0.92. The ASQ and BREESI scales, as well as some validation studies of the aforementioned scales, were excluded from this section because they did not report Cronbach's alpha. These coefficients were analyzed for the purpose of conducting the meta‐analysis, which ultimately included only the HSPS scale. The overall internal consistency was Cronbach's alpha = 0.884 with p < 0.001, indicating the adequacy of this scale. Figure  4 displays the estimates from the individual studies and the overall estimate, as well as the forest plot of the meta‐analysis assessing the global internal consistency of the HSPS. Estimates from individual studies and overall estimate. Forest plot of the meta‐analysis. CI, confidence interval (upper limit/lower limit); FI, forecast interval, (upper limit/lower limit); , Cronbach's alpha for each study; , estimated overall Cronbach's alpha; , estimated overall confidence interval; , Cronbach's alpha confidence interval; , overall effect size value.

This systematic review was performed following the PRISMA statement [ 30 ]. Additionally, a complementary meta‐analysis was performed. The protocol was registered in the PROSPERO database (ID: CRD42023393364). An electronic search of PubMed, Web of Science (WoS), Scopus, Psycinfo, and Cumulative Index to Nursing and Allied Health Literature (CINHAL) was conducted from inception through March 31, 2025. The electronic search was complemented by a manual search, that is, the reference lists of the selected articles and that of this review were screened for studies of interest. In addition, the authors or assessment tools were followed. All the papers that met the inclusion criteria were accepted. Some search terms used in this study were obtained from MeSH (Medical Subject Headings). However, other terms of interest were also included due to their frequent use. The terms applied, and a full list of search strategies, are presented in Table  1 and Table  2 , respectively. Terms grouped by meaning. Note : MESH terms are in italics. Truncations: assess* = assess, assessment; criter* = criteria, criterion; measure* = measure, measurement; person* = person, persons, personality; scor* = score, scoring; *sensitive = sensitive, hypersensitive; *sensitivity = sensitivity, hypersensitivity; valid* = valid, validation, validity. Search strategy. 1 AND 2 AND 3 IN HUMANS JOURNAL ARTICLE ENGLISH, FRENCH, SPANISH TITLE/ABSTRACT 1 AND 2 AND 3 ARTICLE IN ENGLISH, SPANISH, FRENCH TITLE OR ABSTRACT 1 AND 2 AND 3 JOURNAL ARTICLE FROM SCIENTIFIC JOURNAL IN ENGLISH, SPANISH, FRENCH TITLE or ABSTRACT ((“ central sensitization ”  OR  “ central *sensitivity ”  OR  “ sensory‐processing *sensitivity ”  OR  “ sensory processing sensitivity ”  OR  “ highly sensitive person* ”  OR  “ *sensitive person* ”  OR  “ environmental *sensitivity ” OR “temperamental sensitivity” OR “temperamental hypersensitivity” OR “multiple chemical sensitivity” OR “idiopathic environmental”)  AND (scale OR scor* OR questionnaire OR test OR index OR assess* OR examination OR measure* OR outcome OR criter* OR analysis OR evaluation OR rating OR survey OR inventory) AND  (valid* OR reliability)) 1 AND 2 AND 3 ARTICLE JOURNAL (SOURCE TYPE) IN ENGLISH, SPANISH, FRENCH TITLE or ABSTRACT 1 AND 2 AND 3 ACADEMIC PUBLICATION IN ENGLISH, SPANISH, FRENCH TITLE or ABSTRACT Truncations: assess* = assess; assessment; criter* = criteria, criterion; measure* = measure, measurement; person* = person, persons, personality; scor* = score, scoring; *sensitive = sensitive, hypersensitive; *sensitivity = sensitivity, hypersensitivity; valid* = valid, validation, validity. The studies included in this review met the following inclusion criteria: (1) original validation studies, including physical tools or not, based on a conceptual framework created to assess CSS or SPS, in human beings without an age limit; (2) studies reported without a time limit, in English, Spanish, or French, apart from the assessment methods included in the selected studies (scales, questionnaires, tests, etc.), whose presentation was allowed in their language of origin. Note: The physical tools or all the data necessary for their configuration (item statements, partial and total score, interpretation, etc.) could be located in documents other than scientific articles (web, conference proceedings, books, etc.) or by other methods (e.g., request to the authors), which are referenced in the results section to facilitate access to readers. Tools that specifically address a single environmental agent (i.e., noise, odor, etc.) were considered exclusion criteria. The reviewers, NA and GC‐M, separately screened titles and abstracts of the search results to verify whether the studies met the pre‐established inclusion criteria. MB‐M solved the disagreements. The full texts of the studies that met the criteria were acquired, and the causes of any exclusion at this stage were documented. Data extraction, excluding methodological quality, was carried out by one reviewer (MB‐M) and verified by a second reviewer (MS‐F). Data associated with methodological quality, including specific data for meta‐analysis, were extracted by NA and verified by CR‐F. Discrepancies between reviewers were resolved by a third reviewer, GC‐M, who assessed the information independently. The reviewers were not blinded to authors, date of publication, or journal publication. Two predesigned Tables ( 3 and  S1 ) and two standardized Tables ( 4 and  5 ) provide detailed data regarding the selected studies and included tools. The first table (Table  3 ) includes: tool references (name, authors, year, and original language), original validation studies and subsequent validation studies, validation study populations (size and main criteria), further languages through cross‐cultural adaptations (languages, study, authors, years, and notes), descriptions and operating instructions, and observations (e.g., recommendations, location of the physical scales, and bibliographic references of interest). Table  S1 identifies and groups the variables addressed by each tool into different categories. Figure  3 represents the frequencies with which these variables and categories were addressed, thus complementing Table  S1 . Source and characteristics of the assessment instruments. Original validation studies — Other subsequent validation studies Population (n. main criteria) Further languages by cross‐cultural adaptations. Authors. Years. Notes. Descriptions and operating instructions — Observations (recommendations, physical scales, etc.) 1. Adult Sensory Profile (ASP) . Brown et al., 2001 [ 50 ]. English, US . ASP assesses sensory processing patterns and effects on daily life behavior. It consists of 60 items and four subscales with 15 items each: low registration, sensation seeking, sensory sensitivity, and sensation avoiding. Likert scale with five options (1 = almost never, 5 = almost always). Range: 15−75 (each subscale). 75 indicates maximum expressions of the pattern. — Available at commercial editorial [ 129 ] Kinnealey and Oliver, 2002 [ 51 , 52 ]. English, US . Kinnealey and Oliver (2002) Pfeiffer and Kinnealey (2003) [ 51 ] Pfeiffer, Kennealey, Reed, and Herzberg (2005) [ 52 ] ‐Spanish (from Chile) López‐Catalán and Guede (2017) [ 113 ] ASQ detects sensory defensive attitudes. Composed of 26 dichotomous response items (True/False) and four subscales: sensitivity to sensory stimuli (14 items), social emotional behaviors (4), ability to self‐regulate (4), and coping strategies (4). — A score of 10 or above is identified as sensory defensive (Kinnealey and Oliver, 2002). Items and interpretation in the Spanish adaptation by López‐Catalán and Guede (2017) 3. Brief Environmental Exposure and Sensitivity Inventory (BREESI) . Palmer et al., 2020 [ 34 ]. English, US . Palmer et al. (2020) [ 34 ] Palmer et al. (2021) [ 66 ] Palmer et al. (2022) [ 67 ] US (English) BREESI is a brief chemical intolerance (CI) detection instrument. Composed of 3 dichotomous response items (Yes/No): 1 item on chemical exposure (i.e., tobacco smoke, certain fragrances), and 2 items on other chemical exposures (intolerance to foods—i.e., dairy products, caffeine, alcohol beverages, or food additives—and medications—i.e., antibiotics, anesthetics, pain, prothesis, dye), or other medical, surgical/dental material or procedure. BREESI correctly categorized very suggestive and not suggestive. True negative results should be congruent with not suggestive of CI (i.e., no BREESI items chosen) and true positive results should be congruent with very suggestive of CI (3 BREESI items chosen). — The article by Palmer et al. (2020) is a start of the validation (pilot), it is completed in 2021. They recommend using BREESI cut‐off of 3 for epidemiological studies due to its high congruence with CI. 4. Complex Medical Symptom Inventory (CMSI) Schrepf et al., 2018 [ 35 ]. English, US . Schrepf et al. (2018) [ 35 ] 1039. Urologic chronic pelvic pain syndrome. A mixed pain with other COPCs and healthy controls without COPCs. CMSI provided an overall index of the symptoms burden and assesses the presence of chronic functional symptoms. Composed of 41 items with a dichotomous response that evaluates the presence or absence of functional symptoms. Ten of the 41 questions act as “trigger” items, 9 items directly reference pain/tenderness of symptoms central and 22 items cover nonspecific somatic or functional symptoms (somatic awareness subscale, 18 items) or sensory sensitivity to nonpainful environmental stimuli (i.e., to bright lights or odors) (sensory sensitivity subscale, 4 items). Range: 0–18 and 0–4. Higher scores indicate greater presence of chronic functional symptoms. The article by Schrepf et al. (2018) develops a preliminary version of the Brief GSS Scale (Brief Generalized Sensory Sensitivity Scale), which contains a simplified body map with seven regions and six questions about somatic awareness and sensory sensitivity. It assesses the presence of pain and sensory sensitivity. Mayer et al., 2012 [ 36 ]. English, US . Reliability: 149 normative sample Factor analysis: 569 with and without chronic pain (CP) and chronic disabling occupational musculoskeletal disorders. ‐Dutch Kregel et al. (2016) [ 69 ] ϕ, ∆ ‐Spanish Cuesta‐Vargas et al. (2016) [ 70 ] ϕ, # ‐Gujarati Bid Dibyendunarayan et al. (2016) [ 71 ] ϕ ‐Brazilian Portuguese Caumo et al. (2017) [ 72 ] ϕ ‐Japanese Tanaka et al. (2017) [ 73 ] ϕ, # ‐Italian Chiarotto et al. (2018) [ 74 ] ϕ, # ‐Serbian Knezevic et al. (2018) [ 75 ] ϕ ‐Polish Turczyn et al. (2019) [ 76 ] ϕ ‐Greek Bilika et al. (2020) [ 77 ] ϕ ‐Nepali Sharma et al. (2020) [ 78 ] ϕ ‐Korean Kim et al. (2020) [ 79 ] ϕ, # ‐Portuguese Andias and Silva (2020) [ 80 ] ϕ ‐Persian Noorollahzadeh et al. (2021) [ 81 ] ϕ, # ‐German Klute et al. (2021) [ 82 ] ϕ, # ‐Finnish Mikkonen et al. (2021) [ 83 ] ϕ, # ‐Swedish Midenfjord et al. (2021) [ 84 ] ϕ ‐Thailand Wiangkham et al. (2023) [ 85 ] ϕ ‐Arabic Tamboosi et al. (2024) [ 86 ] ϕ, #, ∆ ‐Chinese Tang et al. (2024) [ 87 ] ϕ, # Yin et al. (2025) [ 88 ] ϕ, # CSI assesses the presence of key symptoms associated with central sensitivity syndromes (CSS). It has two parts. Part A is composed of 25 items related to current health symptoms. Likert scale with five options (0 = never, 4 = always). Range: 0−100.100 is the maximum degree of symptomatology. Part B includes information on previously diagnosed CSS and related conditions, indicating the year of diagnosis. Composed of 10 items with a dichotomous response option (Yes/No). — Factor analysis identified a four‐factor solution: physical symptoms, emotional distress, headache/jaw pain symptoms, and urological symptoms. The article by Schrepf et al. (2018) develops a preliminary version of the Brief GSS Scale (Brief Generalized Sensory Sensitivity Scale), which contains a simplified body map with seven regions and six questions about somatic awareness and sensory sensitivity. It assesses the presence of pain and sensory sensitivity. Study 1: 397 nonpatients, patients with CP without CSS; CP patients with diagnoses of CSS. Study 2: 167 patients with at least one CSS and CP Orr et al. (2022) [ 65 ] English, Canada Japanese, Japan . ‐Chinese Liang et al. (2023) [ 108 ] ϕ, ϯ ‐Turkish Bazancir‐Apaydin and Sari [ 109 ] (2024) ϕ CSI‐9 consists of two parts. Part A composed of 9 items. Likert scale with five options (0 = never, 4 = always). Range: 0–36. It is composed of all five components of CSS (CSI): emotional distress, urological and general symptom, muscle symptom, headache/jaw symptoms, and sleep disturbance. Severity is categorized into three levels. A higher score indicated more severe central sensitization CS: subclinical (0−9 points), mild (10−19), and moderate/severe (≥ 20 points). Part B has been used to obtain information regarding a history of CS‐related diseases: restless leg syndrome, chronic fatigue syndrome, fibromyalgia, migraine, multiple chemical sensitivity, neck injury (including whiplash injury), anxiety or panic attacks, and depression. German and English The DOES scale assesses sensory processing sensitivity. Composed of 20 items and four dimensions: depth of processing, overstimulation, emotional reactivity, and sensing the subtle. Likert scale with four options (strongly disagree = 1, strongly agree = 4). Range: 20–80. Higher scores indicate greater SPS. 8. Environmental Hypersensitivity Symptom Inventory (EHSI) . Nordin, Palmquist, Claeson, and Stenberg, 2013 [ 38 ]. Schwedish, Sweden . EHSI evaluates intolerance to various environmental factors, assessing the prevalence of symptoms in various conditions of environmental hypersensitivity (such as odorous or pungent chemicals, nonspecific symptoms related to buildings, everyday sounds, and electromagnetic fields—EMF— among others) and allows comparison with normal rates. Composed of 34 dichotomous items (Yes/No) and five factors related to symptoms: airway (9), skin and eyes (6), cardiac, dizziness, and nausea (4), head‐related and gastrointestinal (5), and cognitive and affective (10). Each factor includes a general item and an extra factor is included with a general item. — Based on the IEISI [ 42 ]. It is Swedish, but it is in English. 9. Environmental Symptom‐attribution Scale (ESAS) . Nordin, Palmquist, and Claeson, 2013 [ 39 ]. Schwedish, Sweden . ESAS assesses the degree to which health symptoms are attributed to specific environmental exposures and sources. Composed of 40 items and four subscales: odorous/pungent (8), building‐related (13), sound (9), and EMF (10). A global score measure is also included. Likert scale with seven options (0 = not at all, 6 = extremely). — The score on the global scale is calculated through the unweighted sum of the 40 items (100/240). The subscales use different factors: 100/48 odorous/pungent, 100/78 for building‐related, 100/54 for sound, and 100/60 for EMF. Each subscale can be used independently and ranges from 0 to 100.100 indicates maximum presence of symptoms. 10. Fear‐Avoidance Components Scale (FACS) . Neblett et al., 2016 [ 40 ]. English, US . ‐Serbian Knezevic et al. (2018) [ 75 ] ϕ, # ‐Spanish Cuesta‐Vargas et al. (2020) [ 110 ] ϕ, # FACS assesses fear of pain and avoidance in patients with painful medical conditions, assessing over the past week what they think and feel about their pain and how it affects their activity level. It consists of 20 items, distributed in three sections: hypervigilance, pain, and avoidance of activities. Likert scale with six options (0 = completely disagree, 5 = completely agree). Range: 0−100.100 is the maximum degree of pain fear and avoidance. — Severity levels for clinical interpretation: subclinical (0−20), mild (21−40), moderate (41−60), severe (61−80), and extreme (81−100). 11. Generalized Pain Questionnaire (GPQ) . Van Bemmel et al., 2019 [ 41 ]. Dutch, Netherlands . Van Bemmel et al. (2019) [ 41 ] GPQ measures and categorizes generalized pain hypersensitivity, assessing the severity of symptoms. Composed of 7 items, seven symptoms commonly associated with generalized pain (i.e., allodynia, secondary hyperalgesia, and subsequent sensations). Likert scale with five options (0 = never, 4 = very strongly). Range: 0−28. — A cut‐off value > 10 is suggested for identifying possible generalized pain hypersensitivity. Spanish (Mexico) . HISS evaluates high interpersonal sensitivity in adults. Composed of 14 items and three dimensions: awareness of subtleties, overstimulation, and persistent effect. Likert scale with four options (1 = not at all, 4 = completely). Range: 14–56. Higher scores indicate greater interpersonal sensitivity. 13. Highly Sensitive Person Scale (HSPS) . Aron and Aron, 1997 [ 16 ]. English, US . Aron and Aron (1997) [ 16 ] ‐German Konrad and Herzberg (2017) [ 89 ] ∆, # ‐Turkish Sengül‐Inal and Sümer (2017) [ 90 ] ∆, # ‐Spanish (Mexican) Montoya et al. (2019) [ 91 ] ∆, # ‐Spanish (Spain) Chacón et al. (2021) [ 92 ] # ‐French Bordarie et al. (2022) [ 93 ] # Polish Baryła‐Matejczuk et al. (2022) [ 94 ] ∆, # ‐English (South Africa) May et al. (2022) [ 95 ] ∆, # ‐Spanish Ponce‐Valencia et al. (2022) [ 96 ] ∆, # ‐Polish Baryła ‐Matejczuk et al. (2023) [ 97 ] ∆, # ‐Spanish Flores‐Vázquez et al. (2023) [ 98 ] # ‐Japanese Iimura et al. (2023) [ 99 ] ∆, # ‐English Pluess et al. (2023) [ 100 ] ∆, # ‐Korean Yang and Kwon (2024) [ 101 ] #,ϯ HSPS evaluates a central variable of sensory processing sensitivity (SPS), high sensitivity in adults, obtaining a total measure of the level of sensitivity in sensory processing. Composed of 27 items. Likert scale with seven options (1 = not at all, 7 = extremely). Range: 27–189. The higher the score, the greater the SPS, that is, the higher the sensitivity. — Factor analyses revealed that the HSPS is a unidimensional construct. Smolewska et al. (2006) [ 29 ] English, Canada. Rinn et al. (2018) [ 68 ] English, US Pluess et al., 2018 [ 55 ]. English, US . ‐Dutch and English Weyn et al. (2021) [ 102 ] ‐ Spanish Costa‐López et al. (2022) [ 103 ] ‐ Dutch Weyn et al. (2022) [ 106 ] ∆, # ‐ Chinese Dong et al. (2022) [ 104 ] Li et al. (2024) [ 107 ] ‐Chinese Ling et al. (2025) [ 105 ]# HSCS evaluates high sensitivity in children and adolescents, obtaining a total measure of the level of SPS. Composed of 21 items and three subscales: ease of excitation (5), low sensory threshold (3), and aesthetic sensitivity (4). Likert scale with seven options (1 = at all/not at all, 7 = extremely). Range: 12−84. The higher the score, the greater the SPS sensitivity of sensory processing, that is, the higher the sensitivity. 15. Highly Sensitive Child‐Rating System (HSCS‐RS) . Lionetti et al., 2019 [ 56 ]. English, US . Observational HSCS‐RS assesses different levels of SPS in highly sensitive children. Captures sensitivity in positive and negative environments, from the framework of environmental sensitivity (ES) and from the theory of SPS. It is applied at children (3−5 years). Composed of 10 scales and seven scenarios, based on the Temperament Assessment Battery (Lab‐TAB) by Goldsmith and Rothbart (1996), designed for children from 6 to 12 months. Likert scale with seven response options (1−7). The higher the score, the greater the ES, that is, the higher the sensitivity. 16. Highly Sensitive Child Interview (HSCS‐I) . Kahkonen et al., 2024 [ 57 ]. Swiss, Switzerland . Interview. Data from parents, children, and teachers . Evaluate children's ES. The version for parents and teachers consists of 17 items and eight responses or reactions: overstimulation, social behavior, response to new situations and changes, sensitivity to the needs and emotions of other people, emotional reactivity, response to physical environment, depth of processing, and response to feedback. The children's version includes similar information (except social behavior), with a smaller number of questions. Responses are scored from 1 to 5. Scores 1 and 2 = response and the examples provided by the interviewee reflect low sensitivity. Score 3 = medium sensitivity and scores 4 and 5 = high sensitivity. Additionally, from the interview, interviewers write down a qualitative impression, noting low, low/medium, medium, medium/high, or high sensitivity. Sperati et al., 2024 [ 58 ]. Italy . HSCS‐PR assesses environmental sensitivity in children through parental report. Composed of 12 items adapted from the Highly Sensitive Child self‐report scale (Pluess et al., 2018) and previously used in a Dutch sample (Slagt et al., 2018). The Italian version (Nocentini et al., 2017) was modified by replacing “I” with “My child.” Three factors: aesthetic sensitivity, low sensory threshold, and ease of excitation. Likert scale with seven options (1 = not at all, 7 = extremely). Range: 12−84. Higher scores indicate greater environmental sensitivity. 18. Idiopathic Environmental Intolerance Symptom Inventory (IEISI) . Andersson et al., 2009 [ 42 ]. Swedish, Sweden . 19. Lynn and Accardi Sensitivity Scale (LASS) . Accardi, 2010 [ 59 ] . English, US . ‐Chinese Shi et al. (2024) [ 114 ] LASS measures psychological sensitivity. LASS explores an individual's awareness and conceptualization of a self as a sensitive person, on a continuum ranging from low to high. The 17‐item version includes three factors: negative self‐evaluation (6 items), emotional sensitivity (7), and social sensitivity (4). Likert scale with five response options (1 = strongly disagree, 5 = strongly agree). Range: 17−85. There are two other versions, composed of 40 and 55 items, with identical factors. Range: 55−275 (55‐item version) and 40−200 (40‐item version). High scores on the negative self‐evaluation subscale may have a low threshold for evaluating oneself in a negative light; on the emotional sensitivity subscale, it represents a low threshold for sensory stimulation, and high scores on social sensitivity would indicate acute sensitivity to other's negative perceptions. 20. Multisensory Amplification Scale (MSAS) . Wang et al., 2022 [ 43 ]. English, US . MSAS assesses multisensory sensitivity. Composed of 12 items and includes five basic systems of multisensory sensitivity: light/vision (2 items), sound/hearing (2), smell (2), tactile (3), and internal bodily sensations (3). Likert scale with five options (1 = not at all true, 5 = extremely true). Range: 12−60. (Men: Q1 ≤ 24, Q2 25–30, Q3 31–35, Q4 ≥ 36; Women: Q1 ≤ 29, Q2 30–34, Q3 35–39, Q4 ≥ 40). 60 indicates maximum expressions of multisensory sensitivity. 21. Quick Environmental Exposure and Sensitivity Inventory (QEESI) . Miller and Prihoda, 1999 [ 44 ]. English, US . Miller and Prihoda (1999) [ 44 ] ‐Swedish, Sweden. Nordin and Andersson (2010) [ 111 ] ‐Spanish Mena et al. (2013) [ 112 ] QEESI evaluates the presence of agents that trigger symptoms, allowing the severity of symptoms and their repercussions on daily life activities to be quantified. Composed of 50 items and five scales, with 10 items each: chemical exposures (inhalation route), other exposures (noninhalation route), symptoms, masking index, or identification of the exposure and impact of multiple chemical sensitivities. All are Likert scales with 11 options (0 = not a problem, 10 = disabling/severely disabling symptoms), except for the Masking Index scale, which is dichotomous (Yes/No). Range: 0−100 (Chemical exposures, other exposures, symptoms, and impact of sensitivities), 0−10 (Masking index). High scores indicate higher levels of environmental exposure and sensitivity. — This scale is a reduced version of the multidimensional Environmental Exposure and Sensitivity Inventory (EESI) instrument (Miller and Prihoda, 1999). It is used as a criterion of severity and evolutionary prognosis of the disease. EESI is composed of five scales from previous instruments. 22. Sensory and Behavioral Modulation Questionnaire (SENSE) . Engel‐Yeger, 2024 [ 45 ]. English, Israel . SENSE assesses responsiveness in everyday life environments and events. Composed of 11 items and three subscales: sensitivity/arousability (3 items), habituation to various stimuli (6), and avoidance (2). Likert scale with five options (1 = always, 5 = never). Range: 11–55. Scores are summarized for each scale and for a total score. Lower scores represent greater sensory and behavioral modulation difficulties. The cut‐off scores for each scale and the total score are defined as one and a half standard deviations above the mean score. Scores lower than 4 on arousability, 10 on habituation, and 3 on avoidance represent atypical performance. 23. Sensory Sensitivity Scale (SHS) . Dixon et al., 2016 [ 46 ]. English, US . SHS assesses both general sensitivity and modality‐specific sensitivity (e.g., touch, taste, and hearing). Composed of 25 items and nine factors: allergies (3 items), heat (2), cold (2), light (3), pain (3), smell (3), hearing (3), taste (3), and touch (3). Likert scale with five options (1 = strongly disagree, 5 = strongly agree). Range: 25–125. 125 is the maximum degree of sensitivity. 24. Sensory Perception Quotient (SPQ). Tavassoli et al., 2014 [ 47 ]. English, UK . SPQ evaluates individual differences in basic sensory perception, without assessing social or emotional aspects. Composed of 35 items and includes the five sensory modalities: vision (6 items), hearing (5), touch (10), smell (10), and taste (4). Likert scale with four options (0 = totally agree, 3 = totally disagree). Range: 0−105. 0 is the maximum degree of sensory sensitivity. 25. Sensory Processing Sensitivity Questionnaire (SPSQ) . De Gucht et al., 2022 [ 60 ]. Dutch, Netherlands . ‐Spanish Salinas‐Quintana et al. (2024) [ 115 ] # SPSQ assesses sensitivity to sensory processing. Composed of 43 items and six factors: sensory sensitivity to subtle internal and external stimuli (SIES) (6 items), emotional and physiological reactivity (EPR) (11), sensory discomfort (SD) (8), sensory comfort (SC) (5), socio‐affective sensitivity (SAS) (8), and aesthetic sensitivity (AS) (5). Likert scale with seven options (1 = not at all, 7 = completely). Range: 43–301. 301 is the maximum degree of sensitivity. — It has two higher‐order factors: positive (SIES, SC, SAS, and AS) and negative (EPR and SC) dimensions. De Gucht and Woestenburg, 2024 [ 61 ]. Dutch, Netherlands . De Gucht and Woestenburg (2024) [ 61 ] . SPSQ‐26 assesses the same things as the original SPSQ and has the same structure and response format. The only difference is the number of items. Gierk et al., 2014 [ 48 ]. German, Germany . Gierk et al. (2014) [ 48 ] SSS‐8 assesses medical conditions related to somatic symptoms and related disorders. Rate the discomfort of symptoms during the last 7 days. Composed of 8 items and four symptom domains: gastrointestinal, pain, cardiopulmonary, and fatigue. Likert scale with four options (0 = not at all, 4 = a lot). Range: 0–32. 32 is the highest degree of somatic symptoms. 28. The Chemical Odor Intolerance Index (CII) . Szarek et al., 1997 [ 49 ]. English, US . Szarek et al. (1997) [ 49 ] The CII assesses how often they experience feeling unwell due to the scent of five different substances: pesticides, paint, perfume, car exhaust, and new carpeting. Likert scale with five options (1 = almost never, 5 = almost always). Range: 5−25. 25 is the highest level of chemical odor intolerance. Davies et al., 2024 [ 62 ]. English, US . 243 families (i.e., mother, partner, and preschool child) TSQ‐scale assesses temperamental sensitivity by assessing children's plasticity in supportive and hostile family environments. Composed of 25 items. Unidimensional. Likert scale with nine options (1 = not at all, 9 = highly characteristic). Range: 25−225. Higher scores indicate greater temperamental sensitivity. Notes : The tools 1, 2, 3, 5, 7, 8, 18, and 28 were found in the gray literature. Instruments published in English, whose original validations are performed in other languages or are not recorded: EHSI [ 38 ], Swedish; GPQ [ 41 ], German; SENSE [ 45 ], Israeli; SPSQ [ 60 ] and SPSQ‐26 [ 61 ], German/Dutch (data provided in the first column). ϕ = the sample involves at least one clinical part; ∆ = the number of items differs from the original version; # = the factorial structure differs from the original; ϯ = the tool has categorizations/cut‐off points (data provided in the fourth column). Abbreviations: ADHD, attention‐deficit/hyperactivity disorder; CI, chemical intolerance; COPCs, chronic overlapping pain conditions; CP, chronic pain; CSS, central sensitization syndromes; ES, environmental sensitivity; IEI, idiopathic environmental intolerance; MCS, multiple chemical sensitivity; SPS, sensory processing sensitivity (data provided in the third column). Availability of the tools: (1) = The original validation only includes the item statements, their scores, and interpretations (data provided in the fifth column). Assessment of methodological quality with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS‐2) tool. Environmental Symptom‐attribution Scale (ESAS; Nordin, Palmquist, and Claeson 2013) Note : Low = low risk of bias or low concerns regarding applicability. High = high risk of bias or high concerns regarding applicability. ? = unclear risk of bias or unclear concerns regarding applicability. Assessment of methodological quality with the Consensus‐based Standards for the selection of health Measurement Instruments Risk of Bias (COSMIN‐RB) tool. Environmental Symptom‐attribution Scale (ESAS; Nordin, Palmquist, and Claeson 2013) The quality assessment of the original validation studies of the included scales and questionnaires is presented in Tables  4 and  5 (see Section  2.4 for Quality Appraisal ). To assess the methodological quality of the included studies, the following instruments were employed: the Quality Assessment of Diagnostic Accuracy Studies‐2 (QUADAS‐2) [ 31 ] and the Risk of Bias checklist developed by the Consensus‐based Standards for the Selection of Health Measurement Instruments (COSMIN RB) [ 32 ]. QUADAS‐2 is an instrument designed to evaluate the methodological quality of diagnostic accuracy studies. It assesses two domains: potential risk of bias and concerns regarding applicability. The risk of bias domain includes the following components: patient selection, index test, reference standard, and flow and timing. On the other hand, the applicability domain includes: patient selection, index test, and reference standard. The seven items that conform the scale can be rated as indicating a “low,” “high,” or “unclear” risk of bias or concerns related to applicability [ 31 ]. QUADAS‐2 is widely used internationally and has been endorsed by the Agency for Healthcare Research and Quality, Cochrane Collaboration, and UK National Institute for Health and Clinical Excellence for inclusion in systematic reviews on diagnosis. On the other hand, the COSMIN RB checklist was utilized to assess the methodological quality of the studies that evaluated Patient‐Reported Outcome Measures (PROMs). This instrument comprises 10 domains, each corresponding to a specific measurement property, and includes items assessing study design quality and the appropriateness of statistical analyses. Evaluations were classified into four qualitative categories: “very good,” “adequate,” “doubtful,” and “inadequate” [ 32 ]. It is worth highlighting that the COSMIN RB tool does not penalize studies for the nonreporting of certain measurement properties (rated as “non‐applicable”: NA); instead, it focuses on those properties that were actually assessed [ 33 ]. A complementary meta‐analysis on the internal consistency of the most representative functional rating scales was conducted using a random‐effects model. For this purpose, the following values were extracted, analyzed, and/or computed: Cronbach's alpha from each validation study, together with measures of dispersion (standard error), p‐value (significance), weighting (%), 95% confidence interval (i.e., type I error was set at 5%, and each relevant parameter was reported with its associated confidence interval, CI), and 95% prediction interval. The p ‐value and the CI of each article and the overall were calculated. The homogeneity test was carried out through the Q ‐statistic, and the heterogeneity test was performed through the H 2 ‐statistic. We also calculated the H 2 index, necessary for the calculation of I 2 heterogeneity (0−100%). Forest plots represented the internal consistency values. The SPSS 28 statistical package (SPSS, Inc.) was used.

Previous literature reports that individuals who develop CSS experience physical, physiological, and psychological health impairments [ 17 ]. In parallel, sustained psychological distress (anxiety, depression, and stress) in individuals with the SPS personality trait due to emotional reactivity is linked to chronic physical and/or physiological symptoms [ 117 ]. Despite this observation, there is a lack of evidence regarding the effectiveness of psycho‐emotional interventions in individuals with CSS or SPS. This could be explained by the lack of diagnostic or assessment instruments with clear parameters that identify individuals with CSS or SPS, categorize their conditions, and allow tracking their evolution. Building on the association between CSS and SPS, the primary objective of this study was to identify and analyze validated CSS and SPS assessment methods (e.g., scales, questionnaires, and tests). As a secondary objective, the current review aimed to conduct an operational comparison of their parameters, content, methodological quality of their original validations, and instructions for use to facilitate the optimal selection for each case. This systematic review gathered 29 CSS and SPS assessment instruments and analyzed the methodological quality of their original validation studies. Of the 29 tools, 16 (55.17%) were associated with CSS [ 21 , 36 , 63 , 64 ], and 13 (44.83%) with SPS [ 49 , 51 , 52 ], as is shown in the results. However, a third condition, that is, environmental hypersensitivity, is worth mentioning for its presence in both CSS and SPS. Six (20.69%) of the 29 instruments were designed to assess intolerance caused by exposure to chemical agents and other environmental sources: BREESI [ 34 ], EHSI [ 38 ], ESAS [ 39 ], IEISI [ 42 ], and QESSI [ 44 ] evaluate both types of agents, whereas CII [ 49 ] exclusively addresses chemical agents. These tools established categories related to various physical health symptoms associated with respiratory pathways and the skin/eyes, among others, in addition to cognitive and affective symptoms. Two of these instruments include a reduced number of items (three for BREESI [ 34 ] and five for CII [ 49 ]). On the other hand, the remaining tools contain between 34 and 50 items. Those with a larger number of items offer more exhaustive information on the factors that lead to intolerance. The assessment instruments were validated in general populations and in specific populations with clinical manifestations or diagnosed pathologies. General populations were considered in 18 (62.07%) original validations, predominantly related to scales addressing SPS content. This may have been due to the fact that high sensitivity is considered a personality trait, without reaching the label of a psychopathological diagnosis. Thus, 11 of the 18 validations directly addressed SPS using DOES [ 53 ], HISS [ 54 ], HSPS [ 16 ], HSCS [ 55 ], HSCS‐RS [ 56 ], HSCS‐I [ 57 ], HSCS‐PR [ 58 ], LASS [ 59 ], SPSQ [ 60 ], SPSQ‐26 [ 61 ], and TSQ‐Scale [ 62 ]. Another six validations considered aspects related to sensory sensitivity through: ASP [ 50 ], which evaluates the sensory profile; MSAS [ 43 ], which assesses multisensory sensitivity; SENSE [ 45 ], which evaluates sensory and behavioral modulation; BREESI [ 67 ], which detects chemical intolerances; and EHSI [ 38 ] and IEISI [ 42 ], which evaluate environmental hypersensitivity. Finally, the validation of SSS‐8 [ 48 ] involved the assessment of somatic symptoms and related disorders, generating a useful instrument for both CSS and SPS. However, specific populations typically corresponded to patients with medical and/or psychosomatic pathologies associated with CSS, as occurred in 11 (37.93%) studies. Of these, six (20.69%) studies used chronic pain as an inclusion criterion, as did Mayer et al. [ 36 ] for CSI and Dixon et al. [ 46 ] for SHS; chronic pelvic pain, as in Schrepf et al.’s [ 35 ] study to validate CMSI; musculoskeletal disorders in the validation of CSI‐9 by Nishigami et al. [ 37 ] and FACS by Neblett et al. [ 40 ]; and fibromyalgia and rheumatoid arthritis in Van Bemmel et al.’s [ 41 ] study for GPQ. Additionally, four instruments included samples with hypersensitivity in ASQ [ 51 , 52 ] and environmental intolerances, as did Szarek et al. [ 49 ] to validate CII, Miller and Prihoda [ 44 ] for QEESI, and Andersson et al. [ 42 ] for IEISI. Tavassoli et al. [ 47 ] included an autism spectrum sample to validate SPQ. Regarding the content addressed by the variables (subscales, dimensions, factors, etc.), and in order of frequency, the categories of psychological aspects and SPS stood out, each with 13 instruments (44.83%). Tools that included variables of psychological aspects, that is, ability to self‐regulate, habituation, emotional distress, hypervigilance, negative self‐evaluation, sensation avoiding, and so on, were: ASP [ 50 ], ASQ [ 49 ], CMSI [ 35 ], CSI [ 36 ], CSI‐9 [ 37 ], FACS [ 40 ], HSCS‐I [ 57 ], IEISI [ 42 ], LASS [ 59 ], MSAS [ 43 ], SENSE [ 45 ], SHS [ 46 ], SPQ [ 47 ], and QEESI [ 44 ]. Similarly, the 13 (44.83%) tools that included variables referring to SPS, such as ease of excitation, aesthetic sensitivity, low sensory threshold, emotional reactivity, sensitivity to sensory stimuli, temperamental sensitivity, and so on, were: ASQ [ 49 ], DOES Scale [ 53 ], HISS [ 54 ], HSPS [ 16 ], HSCS [ 55 ], HSCS‐RS [ 56 ], HSCS‐I [ 57 ], HSCS‐PR [ 58 ], LASS [ 59 ], SPQ [ 47 ], SPSQ [ 60 ], SPSQ‐26 61 ], and TSQ‐Scale [ 62 ]. Physical and psychosomatic symptoms, such as allergies, cardiac symptoms, head‐related symptoms, pain, physical symptoms, and so on, were addressed by 11 (37.93%) instruments: CMSI [ 35 ], CSI [ 36 ], CSI‐9 [ 37 ], FACS [ 40 ], GPQ [ 41 ], IEISI [ 42 ], QEESI [ 44 ], SHS [ 46 ], SSS‐8 [ 48 ], SPSQ [ 60 ], and SPSQ‐26 [ 61 ]. These findings could be explained by the importance, in both CSS and SPS, of psychological variables in understanding suffering, emotional distress, and physical discomfort associated with pain [ 20 ]. This review highlights the relevance of pain assessment in both CSS and SPS, whether by addressing physical, psychological, or emotional components. In this regard, it is worth mentioning that current perspectives on pain have added nociplastic pain to the descriptors of nociceptive pain (associated with tissue damage) and neuropathic pain (due to central nervous system or peripheral alteration). This encompasses regional painful sensations lasting at least 3 months, arising from altered nociception without necessary tissue damage activating peripheral nociceptors, or without a disease or lesion of the somatosensory system producing the pain [ 118 ]. The biopsychosocial model considers this theory and, therefore, the multidisciplinary approach [ 118 , 119 ] advocated by the authors of this study. Thus, the term nociplastic was included by the International Association for the Study of Pain (IASP) in 2017 [ 118 ], for use in a context of central or CS pain, and thus, with inexplicable neuronal hyperexcitation. It should be clarified that nociplastic pain is not a diagnosis but a clinical manifestation, common in patients with fibromyalgia, chronic fatigue, and so on. Consequently, given the relationship this article defends between the existence of CSS and high SPS, a theoretical association with the latter personality trait can be made. Moreover, it is important to consider that several pain descriptors can overlap, for example, nociceptive pain caused by a ligamentous injury and regional nociplastic pain. In fact, if the theories supporting the innate predisposition to hypersensitivity and triggering factors (stress, accident, illness, exposure) are considered, it could even be cautiously asserted that nociceptive pain originating from a severe and chronic musculoskeletal injury may be the origin of nociplastic pain that would add to the clinical picture. These theories lead to considering the need for prospective studies that generate robust evidence. All instruments are PROMs. This suggests the necessity and scientific and clinical interest in understanding and quantifying users’ perceptions across different variables of CSS and SPS. Based on the information defining the characteristics of each instrument, some of them could be discarded (BREESI [ 34 ], CMSI [ 35 ], CSI [ 36 ], CSI‐9 [ 37 ], EHSI [ 38 ], IESI [ 38 ]). However, all statements considered subjectivity in perceiving, attributing, thinking, or feeling, even in instruments that evaluated intolerances or physical problems. In this regard, 27 tools indicated that they were self‐administered. In contrast, other scales or questionnaires address objective, technical, clinical information, and so on, even requiring professional intervention. These are HSCS‐I [ 57 ], which is an interview, and HSCS‐RS [ 56 ], which is observational. Furthermore, all tools included in this study could be complemented by other diagnostic methods such as blood tests to assess inflammatory processes [ 120 ] or physical tests to assess allodynia, like the Quantitative Dynamic Allodynograph [ 121 ]. The 29 tools were distributed into two response modalities for answering the statements. One modality was qualitative, with two response options (Yes/No, True/False, Presence/Absence), and the other was quantitative, using a Likert scale, with several response options to choose the one that best corresponded to each person. Regarding qualitative responses, five (17.24%) tools included dichotomous responses with information on the presence or absence of intolerance to environmental agents, that is, ASQ [ 49 ], BREESI [ 34 ], CMSI [ 35 ], EHSI [ 38 ], and IEISI [ 42 ]; and three (10.34%) more tools, CSI [ 36 ], CSI‐9 [ 37 ], and QEESI [ 44 ], which, in addition to dichotomous items, included multiple response options. As for quantitative assessments, the remaining 21 instruments (72.41%) quantified each possible response, requiring the selection of the most suitable option. Of these, eight instruments included five response options (ASP [ 50 ], FACS [ 40 ], HSCS‐I [ 57 ], LASS [ 59 ], MSAS [ 43 ], SENSE [ 45 ], SHS [ 46 ], and CII [ 49 ]), six instruments included seven options (HSPS [ 16 ], HSCS [ 55 ], HSCS‐RS [ 56 ], HSCS‐PR [ 58 ], SPSQ [ 60 ], and SPSQ‐26 [61]), five instruments included four options (DOES [ 53 ], GPQ [ 41 ], HISS [ 54 ], SPQ [ 47 ], and SSS‐8 [ 48 ]), one instrument included six options (ESAS [ 39 ]), and another instrument (TSQ‐S [ 62 ]) included nine options. All assessment instruments included minimum and maximum scores, with a broader score range observed in tools with multiple response options. Another aspect to note regarding the total scores of the instruments is that, in 27 (93.10%) tools, it was reported that high scores are identified with the evaluated construct. Conversely, SENSE [ 45 ] and SPQ [ 47 ] scores are interpreted in reverse. It is noteworthy that only seven (24.14%) of the instruments indicated cut‐off points (ASQ [ 49 ], GPQ [ 41 ], and SENSE [ 45 ]) or severity levels (BREESI [ 34 ], FACS [ 40 ], HSCS‐I [ 57 ], and MSAS [ 43 ]). All of this is considered fundamental by the authors of this study, as justified in the introduction section and mentioned below when proposing prospective studies. A valuable piece of information, beyond the specific aims of the study, concerns the relationship between the neurobiological correlates of SPS and sensory sensitivity constructs. The scientific literature indicates that SPS is associated with distinctive patterns of brain activation [ 122 ], structural differences in white matter [ 123 ], altered functional connectivity [ 11 , 122 ], and neuroendocrine markers [ 124 ]. Regarding CSS, its neurobiological correlates involve a complex interplay of neural [ 125 , 126 ], neuroendocrine, and psychosocial mechanisms [ 127 ]. These alterations may sensitize peripheral nociceptors, amplifying pain transmission and facilitating CS through long‐term potentiation within the central nervous system [ 128 ]. Therefore, both SPS and CSS appear to be supported by a network of neurobiological features involving brain structure, connectivity, stress physiology, and genetic factors. This finding reinforces, in the case of SPS, its characterization as a distinctive temperament trait that may account for why highly sensitive individuals experience heightened awareness of and reactivity to environmental stimuli. In the case of CSS, it may explain their increased sensitivity to pain perception. The methodological assessment using QUADAS‐2 showed considerable heterogeneity in the quality of the studies included, particularly when comparing older and more recently published instruments. Specifically, the patient selection domain revealed the highest risk of bias, where over half of the studies reached high risk. This trend was frequently identified in those instruments published in the 1990s, which were developed prior to the adoption of structured methodological guidelines. In contrast, more recently published tools showed low risk across all QUADAS‐2 domains [ 37 , 38 , 40 , 48 , 55 , 56 , 58 , 61 , 62 ]. This difference likely reflects the increasing emphasis on rigorous methodological standards of diagnostic test evaluation protocols in contemporary research. Regarding the index test and flow and timing, it showed favorable outcomes across time, which shows that procedures for administering tests were consistently applied. However, the reference standard domain displayed a moderate risk profile, particularly in older studies, highlighting a lack of standardized reference criteria in this area. In this line, the applicability domain showed greater concerns in older studies, whereas recent studies revealed fewer concerns. These findings highlight the importance of study design to enhance the validity and clinical relevance of diagnostic tools. With respect to the methodological quality assessment using COSMIN‐RB, results pointed out that the instruments presented strong psychometric properties across the majority of domains. Nevertheless, some discrepancies among older and newer instruments were found. Tools published after 2010 revealed better adequacy across nearly all domains [ 35 , 36 , 37 , 53 , 54 ]. However, earlier tools frequently lacked the evaluation of reliability and measurement error. The responsiveness domain is considered severely underreported. This absence does not allow for assessing change over time, which is a key psychometric property when assessing outcomes in clinical research. In this regard, it is worth highlighting the Central Sensitization Inventory Short Form developed by Nishigami et al. [ 37 ], which is the only study to assess responsiveness over time. This is also the only instrument that fulfills all COSMIN‐RB domains. The absence of this criterion across the included studies could be explained by the lack of established cut‐off points in the instruments. Similarly, measurement error and reliability were underreported in the studies included in the review. While these findings show significant progress in the methodological quality of recently published articles [ 37 , 53 , 54 ], the lack of responsiveness and measurement errors evidenced gaps that must be addressed in future validation studies. Addressing these issues is essential to ensure that instruments used in clinical contexts are valid, internally consistent, reliable, and sensitive to change. In addition to the methodological quality of the validation studies themselves, this review highlighted the five scales with more than one available validation: CSI, ASQ, BREESI, HSPS, and FACS. The authors conducted an in‐depth examination of their statistical analyses (reliability, internal consistency, construct validity, etc.) with the aim of performing several meta‐analyses. However, the available data only allowed for a meta‐analysis of the internal consistency of the HSPS. Moreover, the lack of homogeneity in inclusion criteria and statistical methods, as well as the repeated use of the same sample, were additional reasons why further meta‐analyses were deemed inappropriate. The conducted meta‐analysis demonstrated that the HSPS showed an overall internal consistency suitable for clinical use. This statistical result supported the HSPS as the most representative scale for assessing SPS in terms of its content.

Regarding the study's limitations, some identified scales/questionnaires had to be excluded, since the tool, or at least a detailed description of its items and instructions for use, could not be located in validation studies or other associated sources. Furthermore, during the study, certain deficiencies were detected in the analyzed publications. As the vast majority was published in English, some authors from non‐English‐speaking countries published their scales/questionnaires in English (see Table  3 and its caption) without clarifying whether these were simple translations or without providing the original validated tools. This leads professionals and readers to erroneously use the English translations in their applications, cross‐cultural adaptations, and so forth. Therefore, it is suggested that the tool in its original language, or at least its location, should be provided, clearly indicating when it is an author's translation and what the original language is. Although this review compiles validated assessment tools to objectively and more easily identify individuals with CSS and/or SPS, only a few instruments established the necessary cut‐off points for this purpose, or at least severity levels (as noted above). Thus, the authors suggest conducting prospective studies that evidence these clinically and research‐relevant data. Additionally, given the relevance and benefits provided by developed questionnaires and scales and their cross‐cultural adaptations, an increase in these adaptations is proposed, consequently expanding their applicability in other population groups by language, clinical aspects, gender, or age, among others. The strengths of this systematic review include not only the comprehensive compilation of CSS and SPS assessment methods, along with their origin, references, and specific characteristics such as components addressed, scoring and interpretation systems, usage guidelines, location of the physical scale, and so on, but also the analysis of the methodological quality of their original validations. Moreover, it includes references for subsequent validations and cross‐cultural adaptations by language conducted to date. All of this aims to provide researchers, clinicians, and educators with an operational document, thereby facilitating the selection of the most suitable tool in each context.

Central sensitivity syndrome (CSS) is a health condition characterized by the overlap of nervous, endocrine, and immune system dysfunction. It is caused by pathophysiological factors such as central sensitization (CS) to various stimuli, immune‐neuroendocrine and autonomic nervous system dysfunction, excessive oxidative stress, and mitochondrial dysfunction, among others [ 1 ]. Of these, CS is considered the fundamental element, and therefore, the genesis of CSS [ 2 ]. CS, which pre‐exists in individuals before they develop symptoms, leads to the hyperexcitability of central neurons and manifests as hypersensitivity to various noxious stimuli received by the central nervous system [ 3 ]. The basis of Yunus’ theory [ 3 ] is based on the bidirectional relationship between the immune system and the central and peripheral nervous systems. Activation of the immune system activates both nervous systems, especially the hypothalamus [ 4 ]. Activated immune cells release proinflammatory cytokines, neural growth factors, or humoral substances such as histamines that activate CS [ 5 ]. In turn, the central nervous system causes hyperexcitation of immune cells. The sensitization of immune cells to different environmental stimuli may affect CS, causing or increasing central dysfunction. Incorrect communication between immune cells (mast cells) and central nervous system cells (neuro‐glia‐microglia) will lead to chronic symptoms [ 6 , 7 ]. On the other hand, the neuroendocrine system (hypothalamus‐pituitary‐peripheral glands) and the autonomic nervous system are altered in CSS, that is, in patients with fibromyalgia or chronic fatigue [ 8 ], mainly due to the corticotropin‐releasing hormone, cortisol, and catecholaminergic pathway. The thyroid axis and growth hormone are also affected. These systems are related to the immune system through cytokines, among other factors. In addition, it has been shown that innate and acquired immune function and the CNS can be activated. This would explain how stress, a factor that acts on the aforementioned systems, could influence immunoneuroendocrine dysfunction [ 9 ]. Environmental sensitivity refers to an individual's capacity to perceive and process information from the environment [ 10 ]. Sensory processing sensitivity (SPS) is a biologically based trait [ 11 ] that manifests as sensory hyperreactivity, causing individuals to perceive environmental stimuli with greater intensity. Emotional reactivity is a fundamental element of this process, referring to the tendency to experience intense or disproportionate emotional responses to external and internal sensory stimuli [ 12 ]. It reflects a complex interaction between the nervous system, sensory perception, and emotional responses. SPS involves deep processing of stimuli and is characterized by a heightened awareness of environmental subtleties, increased emotionality and empathy, and ease of central nervous system overstimulation [ 13 ]. Although different theories and perspectives exist [ 11 , 14 , 15 ], current evidence suggests possible associations between CSS and SPS, particularly regarding their etiologies, associated factors, consequences, and potential interventions. Accordingly, several authors [ 3 , 16 , 17 ] state that an innate predisposition—hypersensitivity in CSS or highly sensitive personality (HSP) in SPS, combined with an environmental trigger (e.g., stress, exposure to chemical substances, electromagnetic fields), diet, infections, and so on—are the causes or drivers of sensitization processes. This leads to CS in the case of CSS [ 18 ] or emotional reactivity in individuals with high SPS (Figure  1 ). Conceptual map illustrating the central sensitization and emotional reactivity processes. In relation to the consequences, the scientific literature links CSS to physical and/or physiological effects that limit and interfere with daily activities. These effects may be exacerbated by the presence of stressful life events [ 19 ]. In contrast, for SPS, sustained psycho‐emotional reactivity (anxiety, depression, and stress) precipitates the chronicity of physical/physiological effects [ 20 ]. Therefore, the psychosomatic effects can be discussed under both conditions [ 21 ]. Unfortunately, most of these consequences have negative health implications that can significantly reduce an individual's quality of life [ 22 ]. In fact, some acquired conditions can become severe and/or chronic, requiring multidisciplinary interventions [ 23 , 24 ]. Based on the aforementioned consequences, psycho‐emotional interventions appear feasible and are recommended in both contexts [ 10 , 25 ]. However, a prior exhaustive review conducted by the authors of this document revealed a deficit of clinical trials addressing the effectiveness of such interventions in subjects with CSS or SPS [ 26 ]. This could, in turn, be attributed to the scarcity of feasible diagnostic tools for daily clinical practice that also interpret scores or provide cut‐off points to identify the presence of CSS or SPS in individuals. Consequently, the execution of clinical trials that include these populations in their inclusion criteria is complicated. Furthermore, the trials identified, such as those by Galvez‐Sánchez et al. [ 27 ] and Nijs et al. [ 28 ], which analyzed psycho‐emotional interventions associated with CSS or SPS, did so based on the increase or decrease in the global score of the scales or their components rather than on the presence or absence of CSS or SPS. Additionally, the scientific literature includes studies, generally cross‐sectional [ 13 ], that use assessment scales to establish associations between variables and compare scores across different population groups (asymptomatic, diabetic, with pain, etc.) [ 29 ]. The results demonstrated an association between CSS or SPS and pathologies, symptoms, and special contexts. In view of this association and the need to know the means of assessment, the main objective of this study was to identify and analyze validated CSS and SPS assessment methods. As a secondary goal, the current work aimed to conduct an operational comparison of their parameters, content, methodological quality of their original validations, and instructions for use, among other elements, to facilitate the best choice in each case.

The authors have no financial or nonfinancial interests to declare.

Supplementary Information : nyas70201‐sup‐0001‐SuppMat.docx