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.