Climate change aggravates atopic dermatitis
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Key takeaways:
- Wildfires and storms were associated with increased rates of clinical visits for atopic dermatitis.
- Drought may disrupt regular health care and cause stress that can exacerbate AD.
Climatic hazards associated with greenhouse gas emissions may exacerbate atopic dermatitis, including severity and flares, while increasing its prevalence and related health care utilization, according to a review published in Allergy.
However, there is a lack of data from the regions of the world most at risk for additional climatic hazards, Katrina Abuabara, MD, MA, MSCE, associate professor of dermatology, University of California, San Francisco, and colleagues wrote.
“Atopic dermatitis, a.k.a. eczema, is particularly sensitive to climatic factors,” Abuabara, who is also an associate adjunct professor of epidemiology at UC Berkeley School of Public Health, told Healio. “Therefore, it’s a natural extension to think about the impact of climate change.”
Most previous research focused on air pollution, with less consensus about how climatic hazards related to greenhouse gas emissions affect AD, she said.
“Therefore, we sought to fill this gap by performing a systematic search and writing a narrative review on the topic,” Abuabara said.
The review comprised 18 studies that linked some aspect of AD to climatic hazards that have been associated with greenhouse gas emissions, including warming, heat waves, drought, precipitation, wildfires, floods, storms, rising sea levels, and ocean climate and land cover changes.
Associations by hazard
The researchers noted that increased temperatures from global warming can induce the production of proinflammatory cytokines and pruritis, aggravating AD. Also, subclinical miliaria due to temperature increases and sweating may precipitate pruritis and AD.
Additionally, the researchers said, warming alters the production, distribution and dispersion of aeroallergens, allergen proteins and air pollutants. However, the four studies in the review that addressed warming and AD had conflicting results.
One study of AD in children in the U.S. indicated an association between poorly controlled AD and higher temperatures and increased sun exposure. But the other three studies found correlations between decreased severity in AD symptoms and increased outdoor temperatures and humidity.
These varying effects on AD may depend on baseline temperature and other climatic or geographic factors, the researchers said.
None of the studies specifically examined the relationship between heat waves and AD, the researchers continued, but they suggested that these extreme weather events may cause psychological and physical stress that may increase AD flares.
Wildfires, which produce significant amounts of air pollution, cause oxidative stress and inflammation in the skin, the researchers said. They also disrupt skin barrier function and aryl hydrocarbon receptor signaling while creating dysbiosis.
In two studies of wildfires and their impact on AD, clinics 175 miles away from a wildfire experienced increases in visits for AD and itch. A third study found increases in Google searches for “itchy,” “eczema” and “red skin” when there were increases in mean weekly particulate matter pollution at the 2.5 µm scale due to a 2020 California wildfire.
There were no studies that directly linked drought with AD, the researchers said, but there may be indirect effects, including food insecurity, poverty, and migration, that disrupt health care and cause physiological and psychological stress that may exacerbate disease. Drought also is associated with wildfires, extreme heat and dust storms, the researchers continued, which may worsen AD as well.
Nine studies of precipitation and AD reported mixed results. One study of children in the U.S. indicated an increased risk for AD with higher mean annual precipitation. Studies from Nigeria and Korea also indicated greater percentages of patients presenting with AD and higher numbers of clinic visits due to AD with more precipitation.
Another study from Korea and a study from Italy, however, only associated rainfall with AD when the daily rainfall totaled less than 40 mm. The other studies did not find any association between precipitation and AD. The researchers suggested, then, that the complex nature of precipitation requires additional studies.
The review also included a study that found increases in AD outpatient visits among all ages during storm periods between 2003 and 2009 in Korea, peaking on day 5 after typhoons, possibly due to sensitization to domestic allergens and psychological distress.
Similarly, townships impacted by flooding caused by Typhoon Morakot in Taiwan in 2009 experienced increased visits for dermatitis in the 8 weeks following the storm. Another study from Taiwan found increased associations between risks for pediatric ED visits for AD and flooding between 2003 and 2015.
A rise in allergenic molds in the atmosphere or allergens and irritants in the flood water may have caused these increases, the researchers said, adding that three other review articles indicated that post-disaster psychological stress may have been an aggravating factor as well.
None of the studies directly examined associations between rising sea levels and AD, the researchers said, but increased risks for flooding and effects on human migration may lead to indirect impacts on disease.
Similarly, there were no studies examining ocean climate change with AD, the researchers continued, but increases in harmful blooms of cyanobacteria and Ostreopsis species may cause irritant contact dermatitis that could lead to AD exacerbations.
Neither of the two studies that examined land cover change found any association between AD prevalence and green space exposure or land cover, the researchers said, but they added that earlier population-based studies found some evidence that AD is more common in urban areas compared with rural areas.
Conclusions, next steps
These findings indicate that most climatic hazards are associated with prevalence, severity and flares and health care utilization in AD, the researchers said, although gaps persist in data and additional research is needed.
“The most significant finding is how little we know about the impact of climatic hazards on atopic dermatitis,” Abuabara told Healio. “We found fewer than two dozen studies that examined direct evidence on the topic, and most were not from the areas most impacted by climate change.”
Most studies also were limited in their subjects, the researchers said, only examining a limited number of hazards, or only health care utilization or disease activity, with a focus on basic mechanisms or epidemiology.
“I think our study highlights the importance of future funding and interdisciplinary initiatives to develop research that can consider multiple climatic factors, integrating basic mechanism with longitudinal outcomes for patients and population-level trends, in diverse populations,” Abuabara said.
Further, she said, most studies looked at health care utilization as an outcome, even though changes in health care utilization may not accurately reflect changes in AD, especially after a climatic hazard.
“Although this may not be surprising to the epidemiologists that study atopic dermatitis, it is important for people to realize how hard it is to study atopic dermatitis in large populations,” Abuabara said.
Many surveys do not ask about skin conditions, nor are there any standard tests with numerical outcomes that would make tracking disease activity or severity over time easier, she said.
“Nonetheless, skin conditions, and atopic dermatitis in particular, can have a huge impact on patients’ lives, so it is important to publicize the need for better data,” Abuabara said.
Further, the researchers said, most of the studies came from the United States. How demographics and other characteristics among patients with AD vary based on the impact of climate change is unclear as well.
New studies should integrate multiple climatic factors and events, the researchers said, while examining their effect on AD incidence, prevalence, and long-term monitoring of disease activity at the patient level.
Also, new studies should expand to cover more geography, particularly areas that are most affected by climate change, and consider differential effects on subpopulations including vulnerable populations.
The researchers additionally said that interventions to improve health may follow studies that can integrate mechanisms with population-level factors such as examining how filaggrin gene mutations interact with air pollution.
“For many patients with atopic dermatitis, not knowing what causes disease flares can be one of the more challenging aspects of the disease,” Abuabara said.
“Although we don’t yet have clear guidance on how patients can mitigate exposures from climatic hazards, physicians may be able to offer anticipatory guidance or practical suggestions around the potential effects of these exposures for their patients,” she said.
Improvements are possible at the policy level as well, with physician participation, Abuabara said.
“Our results add to a wealth of data on the negative health impacts of climate change that physicians can use to advocate for policies that will improve outcomes for patients,” she said.
More specifically, because AD is so common and so clearly linked to environmental factors, it may serve as an opportunity to develop climate-related mitigation policies, she continued.
“In addition, physicians can advocate for more research funding and attention to chronic allergic/inflammatory conditions, which dramatically impact patients’ lives but sometimes do not receive the same attention as conditions like heart disease or cancer,” Abuabara said.
The researchers would welcome the opportunity to continue these investigations.
“We’d love to do a more in-depth quantitative analysis linking global prevalence data with climate models,” Abuabara said. “Moreover, we hope to leverage international collaborations like the International Eczema Council to develop interdisciplinary research collaborations that address some of the gaps we identified.”
Reference:
- How does climate change affect eczema? https://www.eurekalert.org/news-releases/1031905. Published Jan. 24, 2024. Accessed Jan. 26, 2024.
For more information:
Katrina Abuabara, MD, MA, MSCE, can be reached at katrina.abuabara@ucsf.edu.