Beyond the Skin: Atopic Dermatitis and Increased Gastric Cancer Risk in Korea

Background/Objectives: Atopic dermatitis (AD) is a prevalent chronic inflammatory skin disease, but its relationship with gastric cancer (GC) remains unclear. This study aimed to investigate the association between AD and GC using a nationwide Korean database. Methods: Using the Korean National Health Insurance Service-National Sample Cohort, we conducted a nested case–control study including 10,174 GC patients and 40,696 matched controls (1:4 by age, sex, income, and region). Overlap propensity score weighting was used to control for confounders. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated via logistic regression. Results: AD was significantly associated with an increased risk of GC (adjusted OR = 1.08; 95% CI: 1.01–1.15). Subgroup analyses revealed stronger associations among individuals aged ≥ 65 years (OR = 1.12), men (OR = 1.10), rural residents (OR = 1.14), and those without comorbidities (CCI = 0, OR = 1.15). Higher risks were also observed in participants with non-allergic rhinitis (OR = 1.43) or no asthma (OR = 1.12). Conclusions: AD may be associated with an increased risk of GC in the Korean population. These findings may highlight the importance of considering dermatological conditions in the context of systemic cancer risk.