Ambient particulate matter (PM) concentrations and rainfall are independently associated with the number of outpatient visits for atopic dermatitis (AD) in Singapore, according to a study.
Analyses of data on ambient air quality, climate exposure, and AD outpatient consultations from the National Skin Centre (NSC) in Singapore (n=1,440,844) showed a complex interplay between the exposures and the outcome, the investigators said.
“We observed a parabolic dose–response relationship for both PM2.5 and PM10 where AD risk increases up to a threshold and then decreases thereafter,” they continued.
People were 14-percent less likely to see a doctor for AD when PM2.5 levels were low (11.9 vs 16.1 µg/m3: relative risk [RR], 0.86, 95 percent confidence interval [CI], 0.78–0.96), but this likelihood rose by 10 percent at high PM2.5 concentrations (24.4 vs 16.1 µg/m3: RR, 1.10, 95 percent CI, 1.01–1.19). Similar results for PM10 were observed. [Sci Rep 2024;14:10320]
Meanwhile, “the effect of rainfall on the AD consultation visits was positive for values just above the median and negative for extremely high values,” the investigators pointed out.
The likelihood of AD outpatient consultations increased slightly with moderate rainfall, up to 7.4 mm in a model adjusted for PM2.5 (74th vs 50th percentile: RR, 1.07, 95 percent CI 1.00–1.14 ) and 9 mm in a model adjusted for PM10 (80th vs 50th percentile: RR, 1.12, 95 percent CI, 1.00–1.25).
No significant differences were observed when the dose–response relationships for PM, rainfall, and AD consultation visits were compared for male and female subgroups.
These findings indicate that “seasonal variations in particulate matter and rainfall may be used to alert healthcare providers on the anticipated rise in AD cases and to time preventive measures to reduce the associated health burden,” according to the investigators.
Science behind the associations
“To our knowledge, this is the first study conducted in Singapore investigating the associations between air quality and meteorological factors with the incidence of AD consultation visits,” they said.
The associations between PM and AD outpatient consultations are consistent with biologically plausible mechanisms of PM-induced AD exacerbation and onset reported in other studies. Air pollution particles have been found to disrupt the skin’s natural defenses in two ways. First, they damage key proteins, making the skin more vulnerable. Second, they trigger inflammation, which can worsen skin conditions like eczema. [J Dermatol Sci 2018;91:175-183; Toxicol Lett 2017;273:26-35; Toxicol Sci 2016;149:227-236]
“Additionally, PM-exposed skin was found to harbour more Staphylococcus aureus colonies that are known to drive the AD disease cycle,” the investigators pointed out. [Trends Microbiol 2018;26:484-497]
Human behaviour also factors in. For example, very high air pollution levels (>100 µg/m3 for PM2.5) likely lead people to spend less time outdoors and consequently reduce their overall exposure to the pollutant, the investigators explained.
“Moreover, hourly measures of the Pollutant Standards Index are publicly available, and this would have contributed to higher awareness on prevailing PM levels and consequently result in changes in behaviour among Singaporeans. Visual and smell cues from transboundary haze would also have prompted changes in behaviour,” they continued. “In addition, patients with AD are likely to cancel their consultation visits during extreme haze events and stay indoors.”
On the other hand, the effect of rainfall on AD consultation visits is less clear. The investigators postulated that the initial increase in the risk of AD consultation visits above the median rainfall levels may be explained by the higher concentration of allergens indoors. “Additionally, some patients are likely to cancel their appointments during periods of heavy rain, resulting in the decreased risk of AD consultation visits.” [Osong Public Health Res Perspect 2013;4:140-145]
The study was limited by the granularity of the data, with the inability to distinguish between the effects of weather variables in different geographical locations across Singapore.