OBJECTIVE: The objective of this study is to elucidate the causal association between asthma and alopecia areata (AA) through the application of Mendelian randomization (MR) analysis, leveraging summary data from genome-wide association studies (GWAS). Additionally, it explores potential mediating factors. MATERIALS AND METHODS: Mendelian randomization (MR) analysis was employed to investigate the causal relationship between asthma and AA using genetic instrumental variables (IVs) for asthma, 91 circulating inflammatory proteins, and AA extracted from large-scale GWAS. The primary analytical approach utilized the inverse-variance weighted (IVW) method, supplemented by weighted median and MR-Egger methods to assess robustness. Tests for heterogeneity and pleiotropy were conducted to ensure result reliability. Furthermore, the study examined the mediating role of circulating inflammatory proteins in the asthma-AA relationship. RESULTS: The findings revealed an increased risk of AA among asthma patients (odds ratio (OR) = 14.070; 95% confidence interval (CI) = 1.410-140.435; P = 0.024). Interleukin-33 (IL-33) emerged as a significant mediator in the asthma-AA relationship, explaining 13.1% of the mediation effect. Bidirectional Mendelian randomization analyses did not establish a causal effect of AA on asthma occurrence. CONCLUSION: This study, utilizing Mendelian Randomization, elucidates the causal link between asthma and AA, highlighting the mediating role of IL-33. These findings underscore the importance of considering AA risk in asthma management and offer insights for potential therapeutic strategies targeting IL-33. Future research should explore additional biomarkers and mediating mechanisms between asthma and AA to enhance treatment approaches and patient quality of life.