Early Environments, Lasting Effects: Air Pollution, Microbes, and Respiratory Infection Risk in Children

Despite advances in medical care, respiratory tract infections continue to be a leading cause of morbidity and mortality in children worldwide. In addition to posing a healthcare burden, infections acquired early in life are associated with long-term detrimental effects on lung and immune function. This narrative review examines evidence on how environmental factors, such as air pollution and microbes, can affect children's susceptibility to upper and lower airway infections. Epidemiological studies correlate elevated concentrations of ambient and indoor air pollution with a higher frequency of acute upper and lower respiratory tract infections in pediatric populations. Experimental investigations of individual criteria air pollutants such as PM_2.5 demonstrate compromised lung epithelial barrier integrity, oxidative stress and inflammation, and impaired innate and adaptive immune cell function with exposure, all of which may contribute to enhanced infection rates. Concomitantly, the developing respiratory microbiome plays a central role in shaping mucosal immunity; balanced communities provide colonization resistance and support immune education, while dysbiosis driven by antibiotic exposures, air pollution, or other perturbations can predispose to infection and chronic respiratory disease such as asthma. Exposure to diverse environmental microbes, including certain fungi, may also be protective against respiratory illness, and specific microbial signals can confer antiviral benefits. Collectively, the interplay between environmental exposures and infection risk is complex and likely influenced by developmental factors. Policies aimed at improving air quality and strategies to support a healthy microbiome in early life can mitigate the risk of respiratory infections and promote lifelong lung health.