In Louisville, the state’s largest city, several coal-powered industrial plants recently converted to cleaner natural gas. Others installed specialized “scrubbers” to reduce the amount of coal pollution they pumped into the city’s air. For a study published in April 2020 in the journal Nature Energy, researchers looked at the effects these plant conversions had among people with asthma who live in the Louisville area. The study team found that, by the time the last of the power plants had cleaned up their emissions, use of rescue inhalers among the people in the study had dropped by 17 percent. Inhaler use continued to drop by 2 percent each month thereafter, while the amount of air pollution related to coal emissions also fell. The study team found that hospital trips related to asthma also dropped off significantly. “Without a doubt, air pollution can make asthma worse or be a trigger,” says Marsha Wills-Karp, PhD, an asthma researcher and chair of the department of environmental health and engineering at the Johns Hopkins Bloomberg School of Public Health in Baltimore. She says that studies going back decades — both lab experiments and observational work like the Louisville study (which Dr. Wills-Karp was not involved in) — have demonstrated a clear relationship between air pollution and asthma. “Particulate matter is thought to be bad, and also diesel and other chemicals within that pollution,” she says. Multiple sources — factories, motor vehicles, and wildfires, among others — pump these pollutants into the air. But polluted air may contain hundreds of different chemicals or irritants from a variety of sources. Sorting out the specific effects of each one is an ongoing challenge for asthma researchers, she says. Here’s what’s most important for people with asthma to know about how air pollution and climate change can affect the condition — and what they can do about it.
How Air Pollution Makes Asthma Worse
At very high concentrations, air pollution can irritate the airways of the lungs and induce inflammation, which can lead to breathing problems even in people who don’t have asthma. But in the United States, such polluted air is uncommon. Lower concentrations of air pollution, however, still seem to cause trouble for people with asthma. For a paper published in the Lancet, researchers examined how ozone, nitrogen dioxide, fine particulate matter, and other pollutants found in America’s promote asthma-related breathing problems. They say that a handful of things may be going on when the lungs of people with asthma breathe in polluted air. RELATED: Foods That May Trigger Asthma Flares For one thing, pollution may “remodel” airways, stoke existing inflammation, and initiate an immune system response. These factors can both trigger existing asthma symptoms and make them more severe. Over time, regular exposure to air pollution may also create a kind of lung hypersensitivity that makes asthma symptoms worse or more common. In a given person, some or all of these factors may be contributing to that person’s asthma. But the researchers emphasize: “The mechanisms by which pollutants induce these effects are not completely clear.”
Is Air Pollution Causing More People to Develop Asthma?
Another difficult question — one that researchers are also actively investigating — is whether air pollution can cause a person to develop asthma in the first place. While a lot of evidence points in this direction, the connection is not yet solid. “We know that if you’re born or brought up in a place where there’s high pollution, you’re more likely to have asthma,” says Wills-Karp. A study published in 2020 in the European Respiratory Journal that included more than 5,600 children in Canada, for instance, found a link between living in a postal code where concentrations of nitrogen dioxide and ozone were higher and asthma incidence in the kids. “We’ve also found that you can see inflammation in the placenta of mothers who live in high-pollution areas.” Worldwide and in the United States, asthma is much more common than it used to be. And the problem continues to get worse. In 2018, approximately 13 percent of all Americans had been diagnosed with asthma, according to a report from the American Lung Association. In 1999, that figure was just 9 percent. Many researchers have said, the evidence suggests, climate change (and the air pollution it causes) is indeed to blame in part for rising asthma rates. A research review published in December 2015 in the journal Multidisciplinary Respiratory Medicine determined that climate change and a rise in global temperatures may be contributing to both rising air pollution and asthma. According to the review, there is evidence that outdoor air pollution both exacerbates symptoms in people with asthma and that higher levels of outdoor air pollution are associated with higher rates of asthma incidence and prevalence at the population level. Researchers based in China, where air pollution is severe and widespread, reported in a review published in July 2020 in the Chinese Medical Journal that the rise in global asthma rates is at least partly attributable to climate-change factors such as heat waves and wildfires, both of which increase concentrations of particulate matter and ozone in the air. At the 2021 annual meeting of the American Academy of Allergy, Asthma, and Immunology (AAAAI) — which was held virtually in February — Elizabeth Matsui, MD, a professor of population health at the University of Texas at Austin, explained in a presentation that climate change causes heat waves, droughts, and other extreme weather patterns that both exacerbate existing air pollution and also increase the commonness of wildfires, dust storms, and other weather-related events that make air quality worse, and therefore contribute to asthma. But proving that air pollution actually causes, or how much it contributes to, increased asthma incidence — or that climate change is making matters worse — is quite hard to do. Other factors could be at play, too. Wills-Karp points out that, along with asthma, other immune-related medical conditions are also on the rise. Research (including a review published in January 2019 in the International Journal of Molecular Sciences) has linked microbiome imbalances — which may be caused by diet, early life germ exposures, or other non-air-pollution factors — to a heightened risk for both asthma and allergies. “We think air pollution is one of the contributors to the rise in asthma,” she says. “But many roads lead to Rome.” In other words, air pollution and climate change seem to be part of the asthma equation — and maybe a very big part. But other factors are likely involved. RELATED: What Causes Asthma and Asthma Attacks
How to Manage Asthma Triggered by Air Pollution
So, for people whose asthma may be triggered or made worse by air pollution, what options are there to lessen those effects? Wills-Karp says that people who regularly experience asthma symptoms in response to air pollution can usually get relief from inhaled corticosteroids — common medications that reduce swelling and inflammation in the airways. In some cases, bronchodilators and other common asthma remedies can also help. She notes that there are not medications or treatments specifically designed to treat asthma exacerbations linked to air pollution rather than other triggers. “Compliance with medication is one of biggest problems, particularly for people who only have asthma sporadically,” she adds. Other researchers reiterate this point. Also at a session during the 2021 AAAAI annual meeting, Tolly Epstein, MD, an Indiana-based asthma doctor, highlighted poor adherence (or poor access) to asthma medications as a major reason for bad outcomes among adults who have the condition. While experts may eventually discover that certain medications are better suited to asthma symptoms caused by outdoor air pollution, at this point, that kind of targeted treatment isn’t an option. Apart from taking medications, it may help to stay indoors on days when your area’s outdoor air quality is poor. If you check your phone’s weather app, you’ll likely see information related to air quality. The app usually lists the Environmental Protection Agency’s (EPA) air quality index rating for your area. (You can also check the rating for your area at AirNow.gov.) While a rating of 50 or below is considered “good” and associated with “little or no risk,” consider staying indoors on days with an elevated AQI rating (above 50), according to the EPA. Experts will continue to examine and refine the relationship between air pollution and asthma. While a relationship clearly exists, there’s a lot left that they still don’t know.
