Postnasal drip refers to mucus draining from the nose back into the throat. This may be caused by allergies, infections, or other inflammatory conditions of the nose. It is usually treated medically, with nasal sprays or oral allergy medications (or antibiotics when an infection is found to be the cause). Surgical options also exist to open the sinuses if they are found to be the cause, or to lesion the nerve that controls mucus flow from the mucus glands in the nasal lining.