Air pollution may make rheumatoid arthritis flares more likely and drive higher disease activity, according to a new study that identified fine particulate matter, or PM2.5, as the strongest environmental factor.
Published in the Annals of the Rheumatic Diseases, The EULAR Journal, the research indicates that air quality should factor into care decisions for patients with rheumatoid arthritis and into broader public health planning.
Environmental factors and rheumatoid arthritis flares
Rheumatoid arthritis is a chronic autoimmune disease that inflames and damages joints and can cause symptoms throughout the body. It affects about 0.5% to 1% of adults globally and arises from a mix of genetic susceptibility, immune dysregulation, and environmental exposures. Some of these exposures can be modified.
Smoking is already a well-established risk factor. Investigators have also assessed temperature, humidity, silica, and multiple types of pollution. Prior population studies linked polluted air with a higher chance of developing rheumatoid arthritis. Researchers in South Korea set out to determine whether ongoing exposure also influences disease activity and triggers flares in people already diagnosed, and to explore possible biological mechanisms.
In an accompanying editorial, Jeffrey A. Sparks, MD, MMSc, of Mass General Brigham, Brigham and Women’s Hospital, and Harvard Medical School, wrote that this is one of the largest analyses using robust methods to connect air pollutants with rheumatoid arthritis activity. He noted the findings carry clinical, biologic, and public health implications and suggest that inhaled exposures may shape the risk and progression of rheumatoid arthritis and possibly other autoimmune conditions. Clinically, he said, patients may lower flare risk by avoiding poor-quality air.
Tracking exposure and outcomes
The team conducted a prospective cohort study of 1,070 patients with rheumatoid arthritis at a major South Korean medical center. Over four years, from 2021 to 2024, they analyzed data from 12,583 outpatient visits under routine clinical care.
Investigators estimated monthly exposure to six common pollutants: sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), particulate matter 10 micrometers in diameter (PM10), and particulate matter 2.5 micrometers in diameter (PM2.5). They compared these measurements with disease activity and flare outcomes recorded at each visit.
The analysis adjusted for a wide array of potential confounders, including demographics, serologic status, medication use, socioeconomic measures, and weather variables. A sensitivity analysis used a case crossover design based on daily pollutant levels preceding each appointment. With conditional logistic regression, the researchers compared within-person changes to limit bias from time-invariant factors and reduce the chance that disease activity influenced exposure estimates.
PM2.5 stands out in rheumatoid arthritis flares
Lead investigator Eun Bong Lee, MD, PhD, of Seoul National University, said higher PM2.5 concentrations were linked with increased disease activity and a greater risk of flares, particularly with more than two weeks of elevated exposure. Among the pollutants assessed, PM2.5 emerged as the main contributor associated with heightened rheumatoid arthritis activity.
These particles are far smaller than red blood cells. After inhalation, they can move from the lungs into the bloodstream and reach organs throughout the body. The study notes that PM2.5 may drive excessive production of reactive oxygen species, causing cellular stress, DNA damage, and inflammatory signaling that could worsen symptoms and increase flare frequency.
Implications for care and policy
Dr. Lee said the findings have implications for public health policy. While further research is needed to test whether improving air quality reduces disease activity in patients, the authors recommend avoiding prolonged exposure to poor air, especially when PM2.5 levels are high. The researchers emphasized that more studies should examine whether reducing exposure directly lowers disease activity.
ARD Editor-in-Chief Josef Smolen, MD, of the Medical University of Vienna, noted that the paper underwent thorough peer review, with reviewers agreeing on the importance of the results. He cautioned that the observations reflect a Korean population with specific genetic and environmental backgrounds. Confirming whether the findings apply in other regions should be a priority for future work. He added that the study is a valuable starting point for understanding environmental influences on disease activity and treatment responses in rheumatoid arthritis, and a reminder that environmental factors likely contribute to pain and inflammation in affected patients.
Researchers have increasingly focused on how environmental exposures, including air and water quality, shape human health, echoing broader work that examines how landscapes and ecosystems influence communities, as in efforts to create maps without state boundaries to reveal natural ties. Public health planners may look to environmental protection measures and pollution monitoring, including standards set and tracked by the U.S. Environmental Protection Agency, as they consider policies to protect people living with chronic autoimmune diseases.