1. Introduction
Eczema (also known as atopic dermatitis, AD) is a common chronic, recurrent skin allergic disorder in children, with approximately one in five children suffering from eczema. Eczema mostly occurs in early life, with 50% of patients diagnosed within the first year of life(Fishbein, Silverberg, Wilson, & Ong, 2020). In recent years, the incidence of eczema has been on the rise worldwide(Sun et al., 2019), and the intense itching and rash of eczema attacks severely affect the quality of life of affected children(Bosma, Ouwerkerk, & Middelkamp-Hup, 2021). More importantly, children with eczema are more likely to develop other atopic diseases, such as food allergies, asthma, and allergic rhinitis(Hill & Spergel, 2018; Martin et al., 2015). One review estimated that children with eczema are as much as six times more likely to develop a food allergy compared to their healthy peers(Tsakok et al., 2016). Another Canadian study found that children with eczema had 1.65 times the risk of asthma, 7.37 times the risk of food allergies, and 2.36 times the risk of allergic rhinitis at age 3 compared to healthy children(Dharma et al., 2018).
Numerous factors influence the development of eczema in infants and children, including genetic factors and a variety of prenatal and postnatal environmental factors, such as parental allergy history(Venter et al., 2021), maternal diet during pregnancy(Tan et al., 2023), antibiotic use(F. Q. Huang, Lu, Wu, Gong, & Zhao, 2020), and air pollutants. Air pollutants have been shown to increase the risk of allergic diseases, and a 2020 Canadian study showed that NO2 and O3 exposure within the first three years of life increased the risk of asthma and eczema in children(T. To et al., 2020). A Wuhan, China study showed that PM exposure in the early life, especially during pregnancy, increased the risk of childhood asthma(Y. Zhang et al., 2021). A pooled study of two Swedish birth cohorts found that exposure to environmental PM2.5, PM10, and NO2before the age of 2 years was associated with increased expression of inflammatory protein levels such as IL-12B, IL-8, and IFN-gamma(He et al., 2022).
Fewer studies have been conducted on the association between exposure to air pollutants and eczema, and most of them have used the number of eczema outpatient visits as the study outcome. A 2022 time-series study in Guangzhou, China, found that high PM10 exposure in the short term (3 days) increased the number of eczema outpatient visits, with more pronounced effects in children(J. Zhang et al., 2022). A 2022 study in Shanghai, China, found that O3, PM2.5, and NO2 exposure increased eczema outpatient visits, especially in children aged 0-7 years(Ye et al., 2022). A time series study in Chongqing, China, found that short-term (5 days) exposure to ambient air pollutants (PM2.5, PM10, SO2, NO2, CO) increased the number of eczema clinic visits in children aged 0-18 years, especially in children aged 0-3 years(Luo et al., 2022). A 2018 Korean study found that short-term (6 months) exposure to high PM exacerbated atopic dermatitis in preschool children living in industrial urban areas(Oh et al., 2018). A 2015 study from Taiwan, China, found that high CO exposure throughout pregnancy, especially in early pregnancy, increased the risk of eczema in infants at 6 months of life(C. C. Huang et al., 2015). Most of the above studies are about the short-term effects of exposure to air pollutants on eczema, and there is a lack of evidence to assess the effects of long-term exposure to pollutants throughout early life, and the types of pollutants that play a major effect on childhood eczema are not exactly the same in different studies in different regions, moreover, there is a lack of evidence for the combined effects of pollutants. In addition, most of the relevant studies in China are in southern cities such as Guangzhou and Shanghai, and there is a lack of evidence related to the cohort of children in northern cities of China.
Therefore, this study relied on the Jinan birth cohort in a northern Chinese city to investigate the effect of exposure to air pollutants in early life (including pregnancy and two years after birth) on the risk of childhood eczema, and to find its critical window period by distribution lag model (DLM), and to analyze the combined effect of 6 pollutants in different periods by Weighted Quantile Sum (WQS) regression model and Principal component analysis (PCA). The results of the study may provide epidemiological evidence for preventing the development of eczema and improving the physical fitness of children.
2. Materials and methods