Normal mean oral temperature is 98°F, not 98.2°F or 98.6°F

Background 98.6°F is generally accepted as normal body temperature as defined by Wunderlich (1868) and later challenged by Mackowiak (1992) and Protsiv (2020) who concluded as 98.2°F based on cross-sectional studies. Hence, the normal body temperature at present needs quantification? Methods A longitudinal study on the healthy population of Northen-India were followed-up over 1-year. Participants were advised for self-monitoring of oral temperature with a standard digital thermometer in either left or right sublingual pocket and record it in the thermometry diary. The study was considered complete if the participant had all the three phases of the study (i.e. non-febrile, febrile, and post-febrile phases) or completed the duration of the study. Results The mean oral temperature of the participants (n=144) during the non-febrile and post-febrile phases (temperature readings=6543) were 98°F (SD, 0.61) and 98.01°F (SD, 0.60) respectively (P<0.001). The mean oral temperature during post-febrile phase was found to be 0.01°F higher than non-febrile phase. With the diurnal variability, the morning (AM), noon (AN), and afternoon (PM) mean temperatures were 97.91, 98.08, and 98.27°F (P<0.001) respectively during the non-febrile phase. Similar trends were observed in variability among men and women, and seasons. Conclusions The mean oral temperature is 98°F (SD, 0.61). The temperature is as low as 96.9 0 F and as high as 99.1 0 F. The temperature during post-febrile phase was found to be higher than the non-febrile phase temperature like PM over AN & AM, women over men, summer over other seasons in the non-febrile phase, spring over others in the post-febrile phase.