The Epidemiology of Hospital-Treated Alopecia Areata in Denmark, 1995–2016

Alopecia areata (AA) is an autoimmune skin disease presenting as nonscarring hair loss. Information on the epidemiology of AA, especially the occurrence of AA and its subtypes within the general population, is scarce. The study aimed to estimate the incidence rates and prevalence of hospital-treated AA and its subtypes in Denmark and to examine the demographic and clinical characteristics of patients with AA, including comorbidities and use of prescription medications. This was a cohort study based on data from administrative and health registers in Denmark in 1995–2016. The study included individuals who were (1) registered with a hospital inpatient or hospital-based outpatient clinic diagnosis of AA between 1995 and 2016 in the Danish National Patient Registry covering encounters at all Danish hospitals, (2) alive and resided in Denmark anytime between 1995 and 2016, (3) aged ≥ 12 years, and (4) resided uninterrupted in Denmark during the 12 months before the first AA diagnosis during the study period. During the study period, 2778 individuals with an incident hospital-based diagnosis of AA were identified; 63.1