Relevant data, including study design, geographic region, participant characteristics, and results, were extracted from the selected studies. The Newcastle-Ottawa Scale was used to assess the quality of studies and rate them as having low, moderate, or high quality.

The associations between allergic diseases and the risk of lung cancer were assessed using random and fixed effects models. Heterogeneity was evaluated using the I-squared statistic and chi-squared test. Sensitivity analyses indicated that no single study significantly influenced the overall effect size, supporting the robustness of the findings.

The search protocol yielded 226 studies. Following deduplication, title/abstract screening, and full-text reviews, 10 studies were selected for the meta-analysis. Of these, eight were case-control studies and two were cohort studies, cumulatively encompassing over 3.8 million participants.