The Modern Environment and Childhood Asthma: The Role of Air Pollution and Heavy Metal Exposure

Childhood asthma is the most common chronic non-communicable disease in children and a major global public health challenge. Although genetic predisposition contributes to asthma susceptibility, the high burden of disease-particularly in high-sociodemographic-index regions-points to a central role of environmental exposures characteristic of the modern environment. This review synthesizes current evidence linking ambient air pollution and heavy metal exposure to childhood asthma, with a focus on early-life vulnerability, underlying biological mechanisms, and implications for prevention.

We reviewed epidemiological, toxicological, and mechanistic studies published through November 2025, prioritizing systematic reviews and meta-analyses while integrating recent cohort studies, intervention trials, and experimental research. Epidemiological findings consistently demonstrate that prenatal and early-childhood exposure to particulate matter (PM₂.₅, PM₁₀), traffic-related air pollutants (e.g., NO₂, black carbon), and ozone is associated with increased asthma incidence, wheezing, reduced lung function, and higher rates of exacerbations and healthcare utilization. In contrast, evidence for metal-related exposures is more heterogeneous. Toxic metals and metalloids, transition metals in particulate matter, and essential trace-element status may contribute to asthma risk through biologically plausible pathways, but associations appear to depend on exposure timing, exposure source, biomarker type, co-exposures, and population context. Mechanistic studies reveal shared and interacting pathways involving oxidative stress, airway epithelial barrier disruption, immune dysregulation, epigenetic modifications, and microbiome alterations. The effects of these exposures are magnified during critical developmental windows and modified by genetic susceptibility and social determinants of health, contributing to marked environmental health inequities. Overall, childhood asthma is strongly shaped by early-life exposure to air pollution and heavy metals through interconnected biological and social pathways. Addressing these preventable environmental risks is essential for effective asthma prevention and for reducing global disparities.