The Behavioral Immune System in Gender Transition: A Prospective Analysis of Associations Between Sex Steroids and Disgust Sensitivity During GAHT

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Background/Objectives: Experimental and observational studies suggest that sex steroids may modulate disease-avoidance mechanisms and disgust-related responses, but longitudinal evidence in transgender individuals undergoing gender-affirming hormone therapy (GAHT) remains limited. This study investigated whether endocrine changes occurring during the first four months of GAHT were associated with changes in disgust sensitivity, body odor disgust, and perceived vulnerability to disease. Methods: A prospective observational study was conducted in 25 transgender adults (12 transmasculine [FtM] and 13 transfeminine [MtF]) evaluated before initiating GAHT (T0) and after four months of treatment (T1). Participants completed the Three Domains of Disgust Scale (TDDS), the Body Odor Disgust Scale (BODS), and the Perceived Vulnerability to Disease Scale (PVD). Serum testosterone and estradiol concentrations were measured at both time points. Within-group changes were assessed using Wilcoxon signed-rank tests, and associations between hormonal and psychometric changes were explored using Spearman correlations. Results: Among FtM participants, PVD increased significantly following treatment (p = 0.039), whereas no significant changes were observed in pathogen disgust, sexual disgust, moral disgust, or body odor disgust. Greater increases in testosterone were associated with greater reductions in moral disgust (ρ = −0.671, p < 0.05). Among MtF participants, pathogen disgust increased significantly after four months of GAHT (p = 0.015). Greater increases in estradiol were associated with higher moral disgust (ρ = 0.587, p < 0.05) and lower perceived vulnerability to disease (ρ = −0.748, p < 0.01). In addition, testosterone changes were positively associated with changes in sexual disgust (ρ = 0.570, p < 0.05). Conclusions: In this small exploratory cohort, changes in circulating sex steroids during the first four months of GAHT were statistically associated with changes in selected dimensions of disgust sensitivity and perceived vulnerability to disease. The findings are hypothesis-generating and require confirmation in adequately powered longitudinal studies.