For people with conditions such as cystic fibrosis and COPD, mucus can get too thick and sticky; coughing alone can't clear it. Infections develop, leading to severe chronic disease and early death. Now, for the first time, scientists have shown why coughing often cannot tear mucus apart and away from the airway lining. And they showed how to make mucus thinner and less sticky so coughing can become a therapeutic aid.