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

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.