Mixed Results, But Negative Impacts Overall
The researchers identified 18 studies across most of the 10 climatic hazards with evidence for an impact on AD, the majority of which demonstrated harmful effects on various aspects of AD — most commonly on AD-related health care utilization and severity/flares. Only three of the studies examined AD prevalence and notably, none looked at incidence.
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The impact of climatic hazards on AD appears to vary depending on the geographic region and its baseline climate, the authors said. A study in South Korea, for instance, found that in areas declared as disaster zones after storms and heavy rains, the number of AD-related outpatient visits increased for all ages. And a study in the United States showed an increased prevalence of childhood eczema in states with higher mean annual precipitation. However, some other studies on precipitation found no associations.
Just as published studies on precipitation yielded mixed results, so have studies on warming temperatures, Dr. Abuabara and her colleagues reported in their paper, with higher temperatures found to be positively associated with severity of AD symptoms in a study among patients with AD living in a region of Southern Italy, but decreased AD-related health care utilization in a study in Denmark.
In another study of over 5,500 children enrolled in an eczema registry in the United States between 2004 and 2012, higher temperature (odds ratio [OR] = 0.90, P < .001) and increased sun exposure (OR = 0.93, P = .009) were associated with poorly controlled eczema, after the researchers controlled for gender, race, income, and topical medication use.
Studies From 10 Countries Reviewed
Across the 18 studies identified in the review, data were collected in 10 countries. Five studies were conducted in the United States, one used global data, six were from Asia, and the others were from Europe and Africa. Data are lacking, the researchers wrote, in many parts of the world, including coastal regions of the tropics that are projected to experience the largest cumulative climatic hazards.
Future research should not only cover more geographic areas — especially those most impacted by climate change — but should examine impacts on AD incidence, prevalence, and “long-term monitoring of disease activity over time at the individual level,” the researchers recommended. Research should also aim to integrate multiple climatic factors and types of climate data, they said.
“As researchers, we always like to distill things down, but with climatic hazards like warming, you have to integrate other factors such as what the baseline temperature is and how precipitation is involved,” Dr. Abuabara said in the interview. With precipitation, similarly, associated factors such as outdoor humidity, pollen, and pollution exposure may also be at play for AD. Overall, she said, “you have to integrate many types of data.”
In addition to their literature review, the researchers created maps comparing the past, present, and future burden of climatic hazards to AD prevalence data. One pair of maps illustrates global cumulative exposure to climatic hazards in 2005 in parallel with the estimated annual change in AD prevalence in the subsequent decade. “It’s meant to be descriptive,” Dr. Abuabara said in the interview. The maps show alignment “between the areas experiencing the most climatic hazards and those where we subsequently saw the most rapid changes in AD.”
The paper also describes how climatic factors impact skin physiology and AD — exacerbating barrier impairment, immune dysregulation, dysbiosis, and pruritus — and how there are differential impacts on vulnerable and displaced populations with AD. It also briefly addresses air pollution, which was not included in the review framework but is impacted by wildfire and other included climatic factors.