The researchers explained that environmental factors influence AD onset and course, therefore it is imperative to understand the current and potential future climate change impact on patients with AD. Several factors cause patients with AD to be particularly susceptible to environmental impacts, including skin barrier impairment. They noted that most climate research focused on how air pollution impacts patients with AD, so the impact of other climatic hazards has been poorly characterized.

In an interview with The American Journal of Managed Care® (AJMC®), Katrina Abuabara, MD, MA, MSCE, one of the study’s authors, expanded on why this topic was of interest to them.

"I think we've known for a long time that AD is very influenced by environmental factors, and air pollution is a great place to start, but as our recognition of the range of climate impacts broadens, in particular with climate change and the increasing climatic hazards, we felt it was important to fill that gap in the research," Abuabara said.

To fill these research gaps, the investigators searched for studies that specifically examined climatic hazards linked to greenhouse gas emissions and AD on Embase, PubMed, and Google Scholar using related keywords. The researchers chose articles regardless of the year they were published or the language they were written in; they also reviewed the selected articles' citations to identify others not included in their initial search.

The researchers found 18 eligible studies. Seven of these studies measured AD-related health care utilization, 6 measured AD severity and flares, 3 measured AD prevalence, and 1 analyzed AD Google search volume index (SVI). In terms of geographic origin, 6 originated from Asia, 5 from the US, 3 from Europe, 3 from Africa, and 1 used global data from the International Study of Asthma and Allergies in Childhood (ISAAC) Phase 3 Study.

Wildfires | Image Credit: JAH - stock.adobe.com

Global warming, wildfires, precipitation, floods, and storms impact patients with atopic dermatitis (AD). | Image Credit: JAH - stock.adobe.com

From their review, the researchers discovered that many climatic hazards negatively impact patients with AD, causing severity/flares, higher prevalence, and an increase in health care utilization. One climatic hazard analyzed was global warming. Based on the 4 related studies identified, global warming's effects on patients with AD vary depending on the baseline temperature and/or other climatic and geographic factors. One study found that poorly controlled AD was associated with higher temperature and increased sun exposure, while the other studies correlated decreased severity of AD symptoms with increased outdoor temperature and humidity.

The researchers also explained that patients with AD are impacted by wildfire air pollution, which causes inflammation and disruption of the skin barrier function. A Google SVI analysis performed around the California Lightning Complex fire in 2020 found statistically significant associations between a 10 μg/m₃ increase in mean weekly fine particulate matter (PM_2.5) and an increase in mean weekly SVI for AD-related search terms. These findings are consistent with past studies as both short- and long-term ambient PM_2.5exposures have been associated with AD symptoms and dermatological outpatient visits.

Additionally, the researchers identified 9 studies that analyzed the impact of precipitation on patients with AD, which have shown mixed results. One study demonstrated that children living in states with higher mean annual precipitation were at increased risk of having AD. Another study from Nigeria showed that increased precipitation resulted in a higher number of patients presenting with AD. Conversely, in 2 studies from Korea and Italy, only daily rainfall less than 40 mm resulted in increased AD symptoms and severity. These mixed results call for additional research in diverse settings that account for the complex nature of precipitation and other associated factors, like humidity.

Another climatic hazard analyzed was flooding, as the researchers identified 2 relevant studies. One study conducted in Taiwan associated floods with an increased risk of pediatric emergency department visits for AD between 2003 and 2015; they speculated that this may be due to a rise in allergenic molds in the atmosphere or allergens and irritants within the flood water.

Lastly, the researchers analyzed how storms impact patients with AD. They identified 1 Korean study that evaluated the number of outpatient visits for allergic diseases after storms and heavy rains in special disaster zones between 2003 and 2009. AD-related outpatient visits during storm periods increased for all ages (rate ratio [RR], 1.23; 95% CI, 1.22-1.24) and children aged 15 years or younger (RR, 1.27; 95% CI, 1.25-1.28). The researchers theorized that the increase in AD-related visits could be due to psychological distress and sensitization to domestic allergens.

Abuabara explained in an interview with AJMC® the importance of these findings from both a clinical and public health perspective.

"From a clinician perspective, I think one of the hardest things about AD is that it can flare unexpectedly, and that can be very difficult for patients to manage, so understanding different factors that can trigger flares is really important to patients and to clinicians," Abuabara said. "Because AD is so common, it affects up to 20% of kids and 10% of adults around the world, it's worthwhile to understand from a public health perspective how these factors might influence the disease course, how we can better prepare and equip people to handle major climatic hazards, and how that might translate into health outcomes."

The researchers also acknowledged their study’s limitations, one being research distribution inequities. They explained that data on this topic are lacking in many parts of the world, particularly coastal regions of the tropics that are projected to experience the largest cumulative climatic hazards. Also, they did not identify studies with evidence of how heat waves, droughts, rising sea levels, ocean climate change, or land cover change impacted patients with AD. Consequently, the researchers emphasized the need for future research that integrates multiple climatic factors and includes more detailed AD data. Despite the data gaps, the researchers noted that their findings showed that AD could serve as a case study for climatic impacts on health.

“Our study adds to the research on climate change by providing clarity about the extent of research on climatic hazards and AD, including the research gaps and lack of evidence in the locations most impacted now and projected to be most impacted in the future,” the authors wrote.

Reference

Wang S-P, Stefanovic N, Orfali RL, et al. Impact of climate change on atopic dermatitis: A review by the International Eczema Council. Allergy. 2024;00:1-15. doi:10.1111/all.16007