Epidemiology of alopecia areata, ophiasis, totalis, and universalis: A systematic review and meta-analysis.

BACKGROUND

Alopecia areata (AA) is a common autoimmune alopecia with heterogeneous severity and distribution. Previous studies found conflicting results about AA epidemiology.

OBJECTIVE

To determine the prevalence, incidence, and predictors of AA, alopecia totalis, alopecia ophiasis, and alopecia universalis.

METHODS

A systematic review of all published cohort and cross-sectional studies that analyzed AA and its subtypes. MEDLINE, Embase, LILACS, Scopus, Cochrane Library, and GREAT were searched. At least 2 reviewers performed study title/abstract review and data extraction. Random-effects meta-analysis was used because of significant heterogeneity (I = 99.97%).

RESULTS

Ninety-four studies met the inclusion criteria. The pooled prevalence (95% confidence interval, N) of AA overall was 2.11% (1.82-2.42, N = 302,157,365), with differences of population-based (0.75% [0.49-1.06%], N = 301,173,403) and clinic-based (3.47% [3.01-3.96], N = 983,962) studies. The prevalences of alopecia totalis, ophiasis, and universalis were 0.08% (0.04-0.13, N = 1,088,149), 0.02% (0.00-0.06, N = 1,075,203), and 0.03% (0.01-0.06, N = 1,085,444), respectively. AA prevalence (95% confidence interval) increased over time (<2000: 1.02% [0.85-1.22]; 2000-2009: 1.76% [1.51-2.03]; >2009: 3.22% [2.59-3.92]; P < .0001) and differed by region. AA prevalence was significantly lower in adults (1.47% [1.18-1.80]) than children (1.92% [1.31-2.65]; P < .0001).

CONCLUSIONS

AA affects 2% of the global population. AA prevalence is lower in adults than children, is increasing over time, and significantly differs by region.