Androgenetic alopecia risk in allergic rhinitis: A cohort study of immune and antihistamine effects

Background Androgenetic alopecia (AGA), though traditionally attributed to androgens and genetics, is increasingly linked to immune and inflammatory pathways. Allergic rhinitis (AR) and AGA may share overlapping mechanisms, including prostaglandin signaling abnormalities. Second-generation H1-antihistamines (sgSH), used to treat AR, have anti-inflammatory and immunomodulatory properties and may influence hair follicle biology. This study aimed to determine the association between AR and the risk of AGA and to explore whether the use of sgSH impacts this risk. Methods This retrospective cohort study used the Taiwan National Health Insurance Research Database (NHIRD) between 2000 and 2021. Totally, 539,397 patients diagnosed with AR were included and categorized into sgSH users and nonusers. AGA incidence was estimated using Cox proportional hazards models. Results AR patients had a higher risk of AGA (adjusted hazard ratio [aHR]: 1.81, 95% confidence interval [CI]: 1.69–1.93, p < 0.001). Among AR patients, sgSHs users had a lower risk of AGA than nonusers (aHR: 0.23, 95% CI: 0.20–0.26), with a dose-dependent effect ( p < 0.001). The strongest effect seen in patients