It can be the result of several things including colds, allergies, sinus infections and even the flu. In most cases, a stuffy nose is caused by a cold and flu virus that the body typically fights off within a week. Another cause is nonallergic rhinitis, when nasal irritation results from dry air or pollution and not bacteria, viruses or allergies.
Over-the-counter medications can relieve nasal congestion and make it easier for you to breathe.
Decongestants shrink the blood vessels in the lining of the nose and are used to combat stuffiness and can also reduce nasal secretions. Antihistamines work to reduce the amount of runny secretions, but can cause drowsiness.
MORE INFORMATIONSource: http://www.nlm.nih.gov/medlineplus/ency/article/003049.htm