A large prospective study from South Korea has found that exposure to air pollution—particularly fine particulate matter known as PM2.5—is associated with increased disease activity and a higher risk of flares in people living with rheumatoid arthritis (RA). The findings, published in the Annals of the Rheumatic Diseases, suggest that polluted air may influence not only the development of autoimmune disease but also how severely established RA affects patients over time. The researchers say the results could have implications for clinical care, environmental policy and the daily decisions patients make during periods of poor air quality.
Rheumatoid arthritis is a chronic autoimmune disorder in which the immune system mistakenly attacks tissues lining the joints. This produces persistent inflammation, pain, stiffness and progressive joint damage. The disease can also affect organs beyond the musculoskeletal system, including the lungs, cardiovascular system and eyes. Although genetic susceptibility plays an important role, environmental exposures are increasingly recognized as factors that can initiate or intensify abnormal immune activity. Cigarette smoke is a well-established risk factor, while silica, temperature, humidity and other atmospheric conditions have also been linked to RA risk or symptom severity.
Previous epidemiological research has primarily examined whether air pollution increases the likelihood of developing rheumatoid arthritis. The new investigation addressed a different question: once RA is established, can day-to-day or month-to-month changes in air quality influence disease activity and the occurrence of flares? To answer it, investigators followed 1,070 patients receiving outpatient care at a major medical center in South Korea. Together, the patients contributed 12,583 real-world clinical visits over a four-year period from 2021 through 2024, allowing the researchers to compare pollution exposure with changes in symptoms and disease measurements over time.
The study examined six major pollutants: sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide, PM10 and PM2.5. PM10 consists of particles with diameters of 10 micrometers or less, while PM2.5 particles are 2.5 micrometers or smaller—about thirty times narrower than the average human hair. These particles are emitted by sources including vehicle traffic, industrial combustion, construction dust, wildfires and other forms of burning. Because of their extremely small size, PM2.5 particles can remain suspended in the air, penetrate deep into the lungs and interact with biological systems far beyond the respiratory tract.
Researchers matched monthly pollutant concentrations to disease activity and flare outcomes recorded at each patient visit. Their statistical models accounted for a range of potential influences, including age and other demographic characteristics, RA-related antibodies, medication use, socioeconomic conditions and meteorological variables. They also performed a case-crossover analysis based on daily pollution levels before individual visits. This approach compared periods of higher and lower exposure within the same person, helping reduce the impact of factors that remain constant over time and limiting the possibility that worsening disease itself influenced exposure patterns.
PM2.5 emerged as the pollutant most consistently associated with worsening rheumatoid arthritis. Higher concentrations were linked to increased disease activity and a greater likelihood of flares, with the strongest effects appearing after prolonged exposure lasting more than two weeks. The findings do not prove that pollution directly causes every flare, but the consistent relationship across longitudinal analyses suggests that fine particles may be an important environmental trigger for at least some patients. The results also indicate that the relevant exposure window may extend beyond a single day of poor air quality, reflecting the cumulative biological effects of repeated inhalation.
One possible explanation involves the immune and inflammatory consequences of inhaled particles. After entering the deepest regions of the lungs, PM2.5 can activate immune cells and promote the production of reactive oxygen species—highly reactive molecules that can damage proteins, cell membranes and DNA when generated in excess. This oxidative stress can stimulate inflammatory signaling pathways and alter the behavior of immune cells. Because particles and inflammatory mediators may affect the bloodstream and distant tissues, the lungs could serve as an entry point through which air pollution influences systemic autoimmune activity, including inflammation in the joints.
Jeffrey A. Sparks of Mass General Brigham, Brigham and Women’s Hospital and Harvard Medical School, who wrote an accompanying editorial, described the research as one of the largest studies to use robust methods to connect air pollutants with RA disease activity. He noted that the results may help explain apparently unpredictable flares and reinforce the possibility that inhaled environmental substances influence both the risk and progression of autoimmune diseases. From a practical perspective, the findings raise the possibility that limiting exposure during pollution episodes could become one element of flare-prevention strategies, alongside medication adherence and established medical care.
The authors emphasize that further research is needed to determine whether improving air quality or reducing individual exposure can actually lower disease activity. The study was conducted in a South Korean population with a specific genetic background, healthcare system and environmental profile, so its conclusions may not apply equally in every region. Nevertheless, the biological mechanisms are relevant to populations worldwide, particularly as urban pollution, wildfire smoke and climate-related air-quality events become more common. Lead investigator Eun Bong Lee recommends that people with RA avoid prolonged exposure to poor air quality, especially elevated PM2.5 levels, while consulting their healthcare providers about symptom monitoring and treatment. Annals of the Rheumatic Diseases Editor-in-Chief Josef Smolen called the findings an important reminder that environmental conditions may contribute substantially to pain and inflammation in patients with RA.
Subject of Research: People
Article Title: Effects of air pollution on disease activity in patients with rheumatoid arthritis
News Publication Date: 5 August 2026
Web References: https://doi.org/10.1016/j.ard.2026.06.018; https://ard.eular.org/; accompanying editorial: https://doi.org/10.1016/j.ard.2026.07.018
References: Annals of the Rheumatic Diseases, The EULAR Journal; DOI: 10.1016/j.ard.2026.06.018
Image Credits: Sun Hwan Shim
Keywords: rheumatoid arthritis, air pollution, PM2.5, particulate matter, autoimmune disease, inflammation, disease flares, environmental health, oxidative stress, public health
