Association Between Air Pollution and Childhood Asthma: A Systematic Review of Recent Evidence

Background: Air pollution is a major environmental determinant of respiratory health and a significant contributor to the global burden of childhood asthma. Although several recent narrative and systematic reviews have examined environmental triggers of asthma, highlighting air pollution as a consistent risk factor across diverse populations and study designs, recent epidemiological evidence—including multicenter cohort studies and region-specific analyses from Europe and Greece—has not been systematically synthesized. Objective: To systematically review recent epidemiological evidence (2000–2025) on the association between ambient air pollution and childhood asthma incidence and exacerbations, with emphasis on European and Greek populations. Methods: Following PRISMA guidelines, we systematically reviewed observational studies published between 2000 and 2025 in PubMed, Scopus, Web of Science, BMC, and Google Scholar. Studies evaluating quantitative exposure to PM_2.5, PM₁₀, NO₂, O₃, or SO₂ and asthma incidence, prevalence, or exacerbations in children (≤18 years) were included. Evidence was synthesized by pollutant type, exposure window, geographic region, and study design. Results: Twenty-four studies involving more than 3.5 million children were included. Consistent associations were observed across international and European cohorts between long-term exposure to PM_2.5, PM₁₀, and NO₂ and increased asthma incidence. Risk estimates typically ranged from 15% to 30% increases in asthma incidence per 10 μg/m³ increase in long-term exposure to PM_2.5 or NO₂, as reported across multiple cohort analyses. Early-life exposure showed the strongest effects on asthma development and lung function decline. European and Greek studies demonstrated comparable trends, highlighting increased hospitalizations and symptom burden in urban populations despite pollutant concentrations often below current regulatory thresholds. Short-term pollution peaks were additionally associated with increased asthma exacerbations and hospital admissions, particularly during seasonal episodes of elevated particulate matter and ozone concentrations. Conclusions: This review provides an updated synthesis of 21st-century evidence demonstrating that ambient air pollution is a major and modifiable determinant of childhood asthma. The consistency of findings across regions, combined with limited longitudinal evidence from Greece, highlight the importance of improved air-quality management and continued public-health efforts to reduce exposure and the need for enhanced epidemiological monitoring.