Air pollution affects not only respiratory diseases but also rheumatoid arthritis. A domestic study proved that when fine particulate matter increases, arthritis symptoms worsen. Rheumatoid arthritis is an autoimmune disease in which immune cells attack normal cells in the joints. The medical community says prevention policies are needed to have patients with autoimmune diseases avoid areas with poor air quality going forward.
A research team led by Lee Eun-bong, a professor of rheumatology at Seoul National University Hospital, said on the 6th that "the higher the concentration of fine particulate matter, the greater the risk that rheumatoid arthritis suddenly worsens or relapses," in Annals of the Rheumatic Diseases, published by the European Alliance of Associations for Rheumatology (EULAR). The team tracked 12,583 outpatient visits by 1,070 rheumatoid arthritis patients from 2021 to 2024.
◇Of six air pollutants, only fine particulate matter was linked
The researchers analyzed joint pain and swelling, blood inflammatory markers, and other factors in relation to the concentrations of air pollutants in patients' residential areas and at the time of their visits. The six air pollutants were sulfur dioxide (SO₂), nitrogen dioxide (NO₂), ozone (O₃), carbon monoxide (CO), particulate matter 10 micrometers or less in diameter (PM10), and fine particulate matter 2.5 micrometers or less (PM2.5).
The analysis found that among the six air pollutants, PM2.5 was most consistently associated with multiple indicators of rheumatoid arthritis activity. The higher the exposure to PM2.5, the higher the risk of a sudden flare of arthritis. During the study period, the monthly average PM2.5 concentration was 18 micrograms per cubic meter. When PM2.5 increased by 6 micrograms from there, the likelihood of rheumatoid arthritis worsening rose by 11.3%.
Professor Lee said, "This means the odds ratio indicating the risk of arthritis worsening would rise from the usual 1.0 to 1.11, and by itself it is hard to say it triggers a major change," but added, "If exposure continues for more than two weeks, the likelihood of causing problems increases."
The researchers explained that fine particulate matter is smaller than red blood cells, so after entering the lungs it can circulate to distant organs via the bloodstream. In this process, many reactive oxygen species, unstable oxygen byproducts, can form. Reactive oxygen species damage cells and cause aging and disease. The team hypothesized that reactive oxygen species increase inflammatory signaling molecules and trigger inflammation in the joints.
◇First large-scale study in arthritis patients
The medical community evaluated the findings as showing that air pollution must be considered in managing rheumatoid arthritis. Jeffrey Sparks, a professor at Harvard Medical School, said it was "a study that links air pollutants with disease activity in rheumatoid arthritis using robust methods in a large patient population."
Previous studies focused on whether air pollution increases the risk of developing rheumatoid arthritis in healthy people, tracking whether fine particulate matter inhaled into the lungs induces an excessive immune response. Studies have not looked, as in this case, at how fine particulate matter affects patients already diagnosed with rheumatoid arthritis. Such research was conducted in Italy and Iran, but the samples were small and it did not specify which pollutants were problematic.
Professor Sparks said, "This study supports the possibility that substances inhaled through the respiratory tract, such as fine particulate matter, may affect other autoimmune diseases," adding, "It offers important implications for public health as well as clinical and biological significance." For example, when air pollution worsens, it could be possible to issue advisories recommending that arthritis patients refrain from outdoor activities.
Josef Smolen, editor-in-chief of Annals of the Rheumatic Diseases and a professor at Medical University of Vienna, said, "We should keep in mind that these results are limited to a Korean population with specific genetic and environmental conditions," but added, "They show that for the rheumatoid arthritis patients we care for, the environment is likely to act as an essential factor in pain and inflammation."
◇Life expectancy shortened and sperm production also reduced
Fine particulate matter has already been identified as a greater health threat than smoking, traffic accidents, or AIDS. Last year, the Energy Policy Institute at the University of Chicago (EPIC) said global life expectancy had fallen by nearly two years because of fine particulate matter.
The EPIC report found that in 2023, fine particulate matter worldwide was about five times the World Health Organization (WHO) guideline of 5 micrograms per cubic meter, and analyzed that if the WHO standard were met, average life expectancy for all humanity would increase by 1.86 years. This means current air pollution has reduced life expectancy by that much.
The harm from air pollution has long been a global problem. WHO said 90% of the world's population suffers from air pollution and 7 million people die every year. In last year's EPIC report, fine particulate matter was found to be the most harmful risk factor to health, ahead of smoking (1.69 years shorter life), child and maternal malnutrition (1.36 years), traffic accidents (4.8 months), and AIDS (3.4 months).
The harm from air pollution does not stop with the current generation. It threatens the future as well. In 2019, a research team at the University of São Paulo in Brazil published findings showing that fine particulate matter can reduce men's sperm production. In mouse experiments, the team found that the more exposed the mice were to fine particulate matter, the worse their sperm quality became. It was due to diminished function of genes involved in sperm production.
Annals of the Rheumatic Diseases (2026), DOI: https://doi.org/10.1016/j.ard.2026.06.018
Energy Policy Institute at the University of Chicago (2025), https://aqli.epic.uchicago.edu/post/aqli-top-charts-2025-en
Journal of the Endocrine Society (2019), DOI: https://doi.org/10.1210/js.2019-MON-029