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We read the review “Is air pollution a risk factor for rheumatoid arthritis?” with great interest [1]. We agree that air pollution is a potential risk factor for rheumatoid arthritis (RA) in low-and-middle-income countries. As the authors correctly point out, epidemiological studies in high-income countries which have failed to demonstrate a link between air pollution and the risk of RA [2, 3], can not necessarily be generalised to individuals living in lowand-middle-income countries. However, it remains that two large well conducted studies in North America have clearly demonstrated an increased risk of RA in those residing≤ 50 m from a highway compared with residence> 150 m away [4, 5]. This finding is not explained by industrial pollution per se as two studies in high income countries found no consistent association between air pollution and an increased RA risk [2, 3]. If air pollution in high-income countries is not …