Gender- and Genetic-Dependent Sunlight Exposure Effects on the Cumulative Incidence of Atopic Dermatitis during Infancy

Rationale: Sunlight, both Ultraviolet (UV) B and UVA, suppresses the adaptive immunity, but induces the innate immunity in the skin, and then reduces microorganisms. However, it is unclear whether sunlight affects the development of atopic dermatitis (AD) during infancy. Therefore, we investigate associations between sunlight exposure timings and the cumulative incidence of AD in infants.

Methods: Of 1,436 parent-infant pairs, 981 (68.3%) infants over the first 6 months of life without vitamin supplement intake were enrolled in this cross-sectional study in 2009. We assessed postnatal infantile sunlight exposure, a parental family history of allergic diseases (FH) and physician-diagnosed AD by self-writing questionnaires. Sunlight exposure was separated into 3 timings; until the first 6 months of life, over the first 6 months of life and now. We performed statistical analyses by using STATA software.

Results: The recovery rate was 97.2% (1,436/1,476). The cumulative incidence of AD was significantly higher in the infants without sunlight exposure over the first 6 months of life compared with the unexposed infants (25.0% vs 5.68%; P = .030), also in the infants with FH (30.0% vs 5.95%; P = .021). The cumulative incidence of AD was significantly higher in males without sunlight exposure during each timing compared with unexposed males (28.6% vs 6.5%; P = .013: 60.0% vs 6.6%; P = .003: 40.0% vs 6.3%; P = .039), but not in females.

Conclusions: Gender- and genetic-dependently, sunlight exposure might affect the susceptibility to infections mediated by innate immunity in the skin, and then modulate the risk of AD in infants.