Abstract
Childhood is a multifactorial disease, and recent research highlights the influence of early-life microbial communities in shaping disease risk. This review explores the roles of the gut and respiratory microbiota in asthma development, emphasizing the importance of early microbial exposure. The gut microbiota has been particularly well studied, with certain taxa like Faecalibacterium and Bifidobacterium linked to asthma protection, whereas short-chain fatty acids produced by gut microbes support immune tolerance through the gut-lung axis. In contrast, the respiratory microbiota, though low in biomass, shows consistent associations between early bacterial colonization by Streptococcus, Moraxella, and Haemophilus and increased asthma risk. The review also addresses the emerging roles of the skin microbiota and environmental fungi in asthma, though findings remain inconsistent. Timing is a critical factor, with early-life disruptions, such as antibiotic use, potentially leading to increased asthma risk. Despite significant advances, there are still unresolved questions about the long-term consequences of early microbial perturbations, particularly regarding whether microbial dysbiosis is a cause or consequence of asthma. This review integrates current findings, highlighting the need for deeper investigation into cross-organ interactions and early microbial exposures to understand childhood asthma pathophysiology.