In muco-obstructive diseases, such as CF, mucus stasis has largely been attributed to airway dehydration and mucus hyper-concentration (3, 47), but recent evidence shows that electrostatic abnormalities of gel-forming mucins, MUC5B and MUC5AC, also contribute to aberrant mucus physiology (8, 9, 48). Here, MUC5AC is linked to cystic fibrosis.