To evaluate the association between long-term exposure to air pollution and MS risk, as well as short-term exposure and MS severity.

Air pollution has been linked to several neurological conditions, including stroke and neurodegenerative diseases. Evidence regarding its association with multiple sclerosis (MS) remains conflicting, limited by small sample sizes.

We conducted a systematic review and meta-analysis of studies assessing short- and long-term air pollution exposure and MS. Exposures included particulate matter (PM)2.5, PM10, nitrogen dioxide (NO₂), carbon monoxide (CO), sulfur dioxide (SO₂), and ozone (O₃). Outcomes were MS risk, and severity including relapses, disability progression measured with the Expanded Disability Status Scale (EDSS), and contrast-enhancing lesions (CELs) development. Hazard ratios (HRs) with 95% confidence intervals (CIs) were pooled as effect estimates.

Twenty-two studies comprising 16,585,206 participants were included. Long-term exposure to PM2.5 (HR = 1.21; 95% CI: 1.07–1.38), PM10 (HR = 1.20; 95% CI: 1.02–1.42), CO (HR = 3.85; 95% CI: 1.34–11.08), and SO₂ (HR = 3.14; 95% CI: 1.13–8.72) were associated with increased MS risk. Short-term exposure to PM2.5 (HR = 1.20; 95% CI: 1.01–1.43), PM10 (HR = 1.20; 95% CI: 1.01–1.45), NO₂ (HR = 1.13; 95% CI: 1.02–1.25), and O₃ (HR = 1.15; 95% CI: 1.04–1.27) were associated with relapses. Short-term exposure to PM2.5 (HR = 2.20; 95% CI: 1.05–4.60) and PM10 (HR = 1.02; 95% CI: 1.01–1.03) were linked to CELs, while PM10 (HR = 1.31; 95% CI: 1.04–1.65), NO₂ (HR = 1.40; 95% CI: 1.05–1.87), and CO (HR = 1.40; 95% CI: 1.11–1.77) were associated with disability progression.

Long-term air pollution exposure was associated with higher MS risk, and short-term exposure with greater disease severity. Reducing air pollution may be a key strategy to protect brain health in MS.