Nasal congestion, also called sinus congestion or rhinitis, involves blockage of one or more of the four pairs of sinus passageways in the skull. Blockage can result from inflammation and swelling of the nasal tissue, obstruction by one of the small bones of the nose (deviated septum), or from secretion of mucus. Severity can range from acute to chronic, where acute sinus congestion is often caused by the common cold, while chronic sinus congestion often results from environmental irritants such as tobacco smoke, food allergies, inhaled allergens of foreign bodies in the nose.

Without proper attention sinus congestion can lead to impaired flow of sinus fluids, which increases risk of bacterial infections that cause sinusitis. Two serious disorders have been associated with chronic nasal congestion, chronic lymphocytic leukemia and HIV. Severe nasal congestion that lasts three months or more should be evaluated by a medical professional.

Sinus congestion can be a serious problem for many people, typically causing symptoms of pressure, tenderness, or pain in the area above the eyebrows, called the frontal sinus, and above the upper, side teeth, called the maxillary sinus. Other symptoms can include nasal stuffiness that comes with a thick yellow or green discharge, postnasal drip, bad breath, and a dry cough.

Nasal congestion is most commonly caused by allergic reaction to inhalants, such as pollen, molds, dust mites, trees, or animals. There are also known difficulties that arise from various home or workplace chemicals that may contribute to allergic rhinitis. Air pollutants, both indoor and outdoor, may also be a factor in susceptible people.

Nasal decongestants work by decreasing the inflammation in the sinus tissue as well as by relieving blood vessels in the eyes and nose, helping to reduce swelling caused by an allergic reaction, cold or virus. By decreasing the inflammation of mucous membranes, nasal decongestants reduce congestion and stuffiness.