Post‐Acute Sequelae of COVID‐19 on Alopecia Areata in Individuals With Mental Illness in South Korea and Japan: A Binational Population‐Based Cohort Study

ABSTRACT While previous studies have primarily focused on post‐acute sequelae of COVID‐19, the long‐term effects of SARS‐CoV‐2 infection on alopecia areata (AA) among individuals with mental illness remain underexplored. Thus, this study aimed to address this gap by examining the association between post‐acute sequelae of COVID‐19 and AA, with a specific focus on individuals with mental illness. This study utilized bi‐national, large‐scale, and population‐based cohorts of individuals with pre‐existing mental illness: a Korean nationwide cohort (K‐COV‐N cohort; main cohort; total n = 3 248 448) and a Japanese claims‐based cohort (JMDC cohort; replication cohort; total n = 696 332). The outcome focused on the new onset of AA following 30 days after SARS‐CoV‐2 infection, defined using ICD‐10 codes L63. Using a propensity score‐based overlap weighted algorithm, the adjusted hazard ratio (aHR) for AA following COVID‐19 was calculated for individuals with mental illness. In the main cohort, the risk of AA as post‐acute sequelae of COVID‐19 was identified among individuals with mental illness (aHR, 1.32 [95% CI, 1.23–1.43]). The risk was significant for mild mental illness (aHR, 1.33 [95% CI, 1.24–1.44]) and within 6 months postinfection (aHR, 1.48 [95% CI, 1.35–1.63]). Similar findings were observed in the replication cohort. In conclusion, among individuals with mental illness, the risk of post‐acute sequelae of COVID‐19 on AA was elevated—particularly in those with mild mental illness—though this risk decreased over time. Our findings highlight the importance of early screening, integrated care, and equitable healthcare access for managing post‐acute sequelae of COVID‐19.