Decongestants are a type of drug capable of relieving many of the symptoms associated with allergies and colds (e.g., sneezing, coughing, runny nose). They work by reducing the amount of congestion in the nose and sinuses. The two main types of decongestants are pseudoephedrine and naphazoline.

Many allergy symptoms are the result of swollen tissue in the lining of the nose and sinuses and the cellular secretion of fluids into those spaces. These swellings and fluid secretions lead to symptoms such as sneezing, runny nose, red eyes and coughing. The buildup of fluids in the sinuses can cause further pressure and pain.

Decongestants treat the symptoms associated with allergic rhinitis (hay fever), non-allergic rhinitis (colds and flu), sinusitis and allergic conjunctivitis. They do not treat the underlying cause of the symptoms.

Decongestants work by helping to drain the nasal passages. The medication constricts small blood vessels, which reduces secretions into the nose and sinuses. This has the effect of reducing swollen nasal tissue, which opens up the breathing passageways. They also allow the tissue in the inner eyelid to shrink, which reduces eye irritation.