1 | Introduction
Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disorder mostly found in childhood.1 It has become a growing health issue as its prevalence is increased worldwide including Korea.2,3 Besides its grave influence on quality of life, AD also affects the entire family socially and economically.4 Moreover, as an initial manifestation of atopic march, more than 30% of AD patients has been reported to develop allergic rhinitis or asthma in their later lives, with the risk being higher in early-onset, severe, and persistent AD.5,6 AD is also associated with sensitization to inhalant allergens.7,8 Identifying risk factors for severe or persistent phenotype, sensitization, and allergic comorbidities might help establish a better management plan for AD patients.
Among air pollutants, exposure to particulate matter (PM) is associated with adverse health outcomes, especially allergic diseases.9-11 Several studies have already reported that AD symptoms are aggravated by short-term exposure to PM. A longitudinal study involving children aged 1 to 5 years with AD has revealed a significant association between a 10 µg/m3increase in ambient PM2.5 exposure and AD symptoms (adjusted OR [aOR] = 1.399, 95% confidence interval [CI]: 1.216−1.610).12 In another panel study involving 125 AD children aged 0−6 years, the overall risk of AD symptoms significantly increased with higher levels of ambient PM2.5 and PM10exposure.13 In that study, the risk of AD symptoms resulting from exposure to ambient PM was significantly higher during dry, moderate weather as determined by spatial synoptic classification. That study also found a lagged effect of PM2.5 up to 4 days on days with dry, moderate weather. To observe short-term effect of exposure to indoor PM2.5 on AD symptoms, a longitudinal study was conducted on 64 Korean children with moderate-to-severe AD.14 In that study, a 10 µg/m3increase in indoor PM2.5 concentration led to a 16.5% increase in AD symptom scores in spring (95% CI: 6.5−27.5) and a 12.6% increase in winter (95% CI: 4.3−21.5).
Compared to the short-term effect of PM on AD symptoms, studies on the impact of long-term exposure to PM on AD are lacking. A previous study has evaluated the relationship between air pollution and the incidence of AD using the National Health Insurance Service-National Sample Cohort database, including 1,030,324 person-years and 3,203 incident cases. It found that long-term exposure to air pollutants significantly increased the development of AD.15 However, there is very limited evidence of whether long-term exposure to ambient PM affects AD remission or allergic march, particularly in young children.
Thus, this longitudinal study aimed to investigate whether long-term exposure to PM could affect remission of AD at age 3 after the development of AD during infancy. Effect of long-term exposure to PM on aeroallergen sensitization in infants with AD was also evaluated.