Background: The hygiene hypothesis suggests that reduced microbial exposure may contribute to the development of atopic diseases, whereas higher exposure may exacerbate symptoms and promote disease progression.
Objectives: To investigate the association between multiple childhood environmental exposures and atopic multimorbidity, defined as atopic dermatitis (AD) accompanied by at least two other atopic comorbidities, including asthma, food allergy (FA) and allergic rhinitis (AR).
Methods: Data on self-reported, physician-diagnosed lifetime AD were collected in 2020 through a digital questionnaire within the Lifelines Cohort Study, an ongoing population-based study including 167 729 residents of the northern Netherlands. Adults retrospectively reported childhood environmental exposures, including birthweight, gestational age, delivery mode, breastfeeding, tobacco smoke exposure (maternal or childhood), cat or dog ownership before the age of 16 years (ever owned, type and age at ownership) and living conditions. All exposure data, along with data on asthma, AR and FA, were collected between 2006 and 2013. Associations between environmental exposures and atopic multimorbidity (vs. no atopic disease) were assessed using logistic regression, adjusted for age, sex, socioeconomic status, parental history of asthma and sibling status.
Results: Among 28 791 included participants, 27 939 (97.0%) reported no atopic diseases, while 852 (3.0%) reported atopic multimorbidity. Compared with participants without atopic diseases, caesarean section delivery was positively associated with atopic multimorbidity [odds ratio (OR) 2.55, 95% confidence interval (CI) 1.20-5.46], whereas pet ownership before the age of 16 years (OR 0.52, 95% CI 0.37-0.75), including ownership of dogs only (OR 0.59, 95% CI 0.37-0.94), cats only (OR 0.44, 95% CI 0.26-0.74) or both (OR 0.53, 95% CI 0.34-0.83), was negatively associated with atopic multimorbidity.
Conclusions: Childhood pet ownership may be protective against atopic multimorbidity, whereas caesarean section delivery may be associated with a higher likelihood of atopic multimorbidity, providing insights into potential preventive strategies.