A review of the effects of valenced odors on face perception and evaluation

How do valenced odors affect the perception and evaluation of facial expressions? We reviewed 25 studies published from 1995 to 2020 on cross-modal effects between olfaction and facial perception. The results indicate that odors may influence facial evaluations and classifications in several ways. Faces are rated as more arousing during simultaneous odor exposure, and the rated valence of faces is affected in the direction of the odor valence. For facial classification tasks, in general, valenced odors, whether pleasant or unpleasant, decrease facial emotion classification speed. The evidence for valence congruency effects was inconsistent. Few studies found that exposure to a valenced odor facilitates the processing of a similarly valenced facial expression. The results for facial evaluation were mirrored in classical conditioning studies. Faces conditioned with valenced odors were rated in the direction of the odor valence. However, the evidence was inconsistent in facial classification tasks in this literature. Although the research shows some clear patterns, other effects are mixed. Our future research recommendations include greater consideration of individual differences in sensation and cognition, individual differences (e.g., differences in odor sensitivity related to age, gender, or culture), establishing standardized experimental assessments and stimuli, larger study samples, and embracing open research practices.