Probing the impact of gender-affirming hormone treatment on odor perception.

Evidence suggests that women outperform men in core aspects of odor perception, and sex hormones may play a significant role in moderating this effect. The gender-affirming treatment (GAT) of transgender persons constitutes a powerful natural experiment to study the psychological and behavioral effects of high dosages of cross-sex hormone applications. Therefore, our aim was to investigate the effects of GAT on odor perception in a sample of 131 participants including female and male controls, as well as transmen and transwomen over their first 4 months of gender transition. The Sniffin' Sticks test battery was used to measure odor detection, discrimination, and identification at baseline, as well as 1 and 4 months after the start of GAT. Plasma levels of estradiol, testosterone, and sex hormone-binding globulin were analyzed for each assessment point. Results revealed no significant change of olfactory performance in the two transgender groups compared with female and male controls. There was no significant difference between groups at baseline or any other time point. Neither biological sex, nor gender identity had an influence on odor perception. Moreover, there was no significant correlation between sex hormones and odor perception and between GAT-induced changes in sex hormones and changes in odor perception. Our results indicate that the effects of sex hormones on olfactory performance are subtle, if present at all. However, our results do not preclude hormonal effects on odors not included in the Sniffin' Sticks test battery, such as body odors or odors associated with sex.