Additional methods and results of : "Caesarean Section and Atopic Dermatitis Risk: Insights from a Nationwide, Population-based Cohort Study"

Atopic dermatitis (AD) is a chronic inflammatory skin condition that causes recurrent skin pruritus and eczematous lesions and results in erosion, excoriation, and lichenification, impacting the patient’s quality of life. A recent systematic review showed that the composition of gut and skin microbiomes is distinctly different between people with AD and those without AD, which may be related to early exposure to the microbiome via different birth delivery methods. Although previous studies have established associations between cesarean section (C-section) and allergic diseases, such as asthma and food allergies, they have not reached a consensus on whether the association can be applied to AD, the earliest manifestation of the atopic march. Recent studies have reported varying odds ratios, ranging from 0.70 to 1.57, for the association between C-section and AD. However, most previous studies are limited by insufficient sample sizes and follow-up durations. In this study, we aimed to investigate the association between birth delivery mode and the incidence of AD by linking the population-based national health insurance claims database and the birth registry in Taiwan. To the best of our knowledge, this is the first report on examining the C-section and AD risk with a large database of 1 534 384 children born between 2005 and 2013, and long follow-up duration until 2020. We found that children delivered via C-section exhibited a significantly higher AD incidence than vaginally delivered counterparts (adjusted hazard ratio (aHR): 1.021 [95% CI: 1.014–1.028; P < .0001]). Parental atopy, gestational diabetes, intrapartum antibiotics, and male gender were identified as common risk factors for AD in both C-section-delivered and vaginally delivered groups. Our findings highlight the importance of considering delivery method, maternal comorbidities and children’s sex in assessing the likelihood of AD development. These findings underscore the need for personalized approaches in obstetric and pediatric care, enhancing our ability to proactively address AD and improve overall clinical outcomes.