A stuffy or congested nose occurs when the tissues lining the nose become swollen. The swelling is due to inflamed blood vessels. The problem may also include nasal discharge or "runny nose." If excess mucus runs down the back of your throat, it may cause a cough or sore throat. A runny nose may be annoying and uncomfortable, but it usually clears up on its own. Occasionally, it can be a sign of a more severe problem. A runny nose may be severe in infants.