The epidemiology of alopecia areata: a population-based cohort study in UK primary care.

Background There is a lack of population-based information on the disease burden and management of alopecia areata. Objective To describe the epidemiology of alopecia areata, focusing on incidence, demographics, and patterns of healthcare utilisation. Methods Population-based cohort study of 4.16 million adults and children, using UK electronic primary care records from the Oxford-Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) network database, 2009-2018. Incidence and point prevalence of alopecia areata was estimated. Variation in alopecia areata incidence by age, sex, deprivation, geographical distribution and ethnicity was examined. Patterns of healthcare utilisation were evaluated in people with incident alopecia areata. Results Alopecia areata incidence was 0.26 per 1,000 person-years. Alopecia areata point prevalence in 2018 was 0.58% in adults. Alopecia areata onset peaked at age 25-29 for both sexes, although the peak was broader in females. People of non-white ethnicity were more likely to present with alopecia areata, especially those of Asian ethnicity (Incidence rate ratio 3.32 [95% confidence interval 3.11-3.55]). Higher alopecia areata incidence was associated with social deprivation (IRR most vs least deprived quintile 1.47 [1.37-1.59]) and urban-living (IRR 1.23 [1.14-1.32]). People of higher social deprivation were less likely to be referred for specialist dermatology review. Conclusion By providing the first large-scale estimates of the incidence and point prevalence of AA, our study helps to understand the burden of AA on the population. Understanding the variation in AA onset between different population groups may give insight into the pathogenesis of AA and its management.