Introduction
Changes in the prevalence of atopic dermatitis (AD) according to age in Korean children have been observed. Although the development of AD during infancy is decreasing, prevalence in late childhood is increasing, indicating rising rates of late-onset or early-onset phenotypes (1). AD is a persistent disease with a high burden on children and their families. In combination with genetic factors, environmental influence is an important contributor to the pathogenesis of AD, indicating the importance of early interventions to improve or prevent AD outcomes(2).
Smoking during pregnancy is a well-established risk factor for adverse outcomes such as low birth weight (3), spontaneous abortion(4), and preterm birth (5) and wheezing (6). However, the proportion of active smokers among pregnant women in Korea is comparatively lower than that in western countries. A study conducted in South Korea reported that 0.55% of mothers admitted to actively smoking, while 3.03% were considered to be actively smoking based on their urine cotinine levels (7).
Approximately 35%, 33%, and 40% of nonsmoking females, males, and children are exposed to SHS daily (8). In Korea, 60.4% of pregnant non-smokers reported exposure to SHS during pregnancy(9). The Cohort for Childhood Origin of Asthma and Allergic diseases (COCOA) study revealed that prenatal SHS exposure increases susceptibility to lower respiratory tract infections in infancy(10). Given that AD is a disease affected by environmental factors, the possibility for SHS to be a potential contributor could not be ruled out.
Therefore, we investigated the relationship between prenatal SHS exposure and AD across various groups and the effects of sensitization in a prospective birth cohort study. Additionally, we aimed to validate our findings by determining the relationship between urine cotinine levels during pregnancy and AD.