Mucus is an essential protective layer of gel-like liquid composed largely of proteins called mucins throughout our airways. One of them, called MUC5B, is crucial for the innate defense against the various things we inhale. But another mucin, called MUC5AC, generally increases disproportionately in response to cigarette smoke and allergens, adding to health problems. For the first time, scientists at the UNC School of Medicine have discovered how MUC5AC emerges to disrupt airways of individuals suffering from lung conditions, such as chronic obstructive pulmonary disease (COPD) and asthma.