Exposure to PM2.5 pollution is associated with an increased disease activity and flare risk in rheumatoid arthritis, a chronic autoimmune disease marked by joint inflammation and joint damage, according to a new study. Over 1,000 patients with rheumatoid arthritis from across 12,583 outpatient visits over four years (2021-2024) at a South Korean medical centre were tracked. PM2.5 was identified as a key contributor to increased disease activity in rheumatoid arthritis. "Among (the) six pollutants, PM2.5 was significantly associated with an increased risk of flare and with (a) higher Disease Activity Score based on 28 joints (DAS28) with C-reactive protein (CRP), Clinical Disease Activity Index, 28-tender joint count, and 28-swollen joint count," the authors wrote. Further, a prolonged cumulative exposure to PM2.5 over more than two weeks was associated with an increased risk of flare in rheumatoid arthritis.