The lungs are a fragile organ in which development begins in-utero and continues until early adulthood. Both infections and changes to the microbiome can effect development leading to chronic diseases such as asthma and COPD. However, the period when infection occurs , pathogen causing the infection, and the severity of the infection are important. For example, the lungs are particularly vulnerable in-utero, but severe viral infections in the first two years of life cannot be ignored either. This presentation will use asthma as a archetypical lung disease and discuss the interplay of commensal and pathogenic organisms on lung development. It will also highlight a simple non-invasive way to collect samples from the lungs.