Global sex disparities in lifetime risk of alopecia areata: a systematic analysis from the global burden of disease study, 1990 to 2021.

Background: Alopecia areata (AA) represents a significant autoimmune disorder affecting hair follicles, with sex differences that have yet to reach scientific consensus. The regional and temporal, age-related, and socioeconomic dimensions of sex-based lifetime risk disparities remain inadequately characterized and require further investigation.

Methods: (1) We estimated AA lifetime risk using the adjusted for multiple primaries method. We evaluated regional and temporal features of sex disparities through Average Annual Percentage Change analysis, with future projections to 2050 via ARIMA modeling. (2) Age-stratified sex disparity features were analyzed. (3) We evaluated AA risk associations with Socio-Demographic Index (SDI) variations through Spearman correlation analysis and concentration indices to quantify female-to-male relative risk.

Results: (1) Global lifetime risk increased from 29.89% (95% CI, 29.83%-29.94%) to 31.66% (31.61%-31.71%) in females, and from 15.91% (15.86%-15.95%) to 16.93% (16.88%-16.97%) in males between 1990 and 2021. The female-to-male lifetime risk ratio remained stable, measuring 1.88 (1.87-1.89) in 1990 and 1.87 (1.86-1.88) in 2021. Future projections through 2050 indicate increasing lifetime risks reaching 34.44% (32.99%-35.89%) for females and 19.06% (17.50%-20.63%) for males, despite comparatively faster growth rates observed in the male population (9.83% vs. 7.01% for females). Both sexes exhibited similar regional distribution features. (2) Sex differences in age-specific risk features were notable: females exhibited a high lifetime risk window between ages 20-50 years, while males demonstrated a narrower window primarily between ages 20-30 years. Female lifetime risk consistently peaked in the 30-39 age group regardless of SDI level, whereas males displayed significant SDI-dependent variations, with peak lifetime risks occurring at ages 20-29 in high-SDI regions versus ages 30-39 in the other areas. Females showed a slower decline in residual risk with increasing age compared to males, resulting in progressively higher female-to-male risk ratios that were particularly pronounced in high-SDI regions, reaching 4.51 (3.42-5.95) in the 70-79 age cohort. (3) With increasing SDI levels (reflecting socioeconomic development), females exhibited more pronounced risk elevation than males. Females exhibited consistently lower concentration indices relative to males, maintaining stable trends, while male concentration indices have shown a declining trend in recent years. The female-to-male ratio of concentration indices has shown a consistent upward trend since reaching its lowest point of 0.62 (0.51-0.76) in 1993, rising to 0.75 (0.60-0.95) by 2021. High SDI regions persistently demonstrate the lowest female-to-male concentration indices.

Conclusions: Our analysis reveals pronounced sex disparities in global AA lifetime risk: consistently higher risk in females across regions and time periods, prolonged age-related risk window with slower decline in females, and greater risk elevation in females with increasing SDI levels.