Associations between Residential Indoor Environmental Indicators and Respiratory Allergic Symptoms Among Children in Shenzhen, China

Children are particularly vulnerable to indoor environmental exposures, yet evidence based on residential measurements remains limited. This study assessed associations between 22 indoor environmental indicators and respiratory allergic symptoms in children using 115 observations from Shenzhen during 2023–2024. Single-pollutant logistic regression, restricted cubic spline, and weighted quantile sum regression were applied, adjusting for age, sex, body mass index, family history of allergy, and indoor temperature, except when temperature was the exposure. Asthma-related and allergic rhinitis-related symptoms were reported in 35.7% and 47.8% of observations, respectively. Higher indoor temperature and illuminance were associated with increased risks of both outcomes. O₃, total volatile organic compounds, SO₂, toluene, and total bacterial count were inversely associated with allergic rhinitis-related symptoms. Relative humidity and total fungal count were positively associated with allergic rhinitis-related symptoms only in the basic adjusted model, while medium formaldehyde exposure was associated with increased asthma-related symptoms. Nonlinear associations were observed for air velocity with both outcomes and for relative humidity and total fungal count with allergic rhinitis-related symptoms. No significant overall mixture effect was identified. These findings indicate that physical, chemical, and biological indoor factors may contribute differently to childhood respiratory allergic symptoms and warrant confirmation in larger longitudinal studies.