Nasal polyps are noncancerous, painless teardrop-shaped growths that form on the lining of your nasal passages or sinuses and, when mature, can resemble seedless, peeled grapes.
Nasal polyps are often associated with allergies or asthma and may cause no symptoms, particularly if they are small. Larger growths or groups of nasal polyps, however, can block normal drainage from the sinuses or lead to breathing problems, a loss of the sense of smell and frequent infections from mucus accumulated in the sinuses.
Similar to an asthmatic reaction in terms of their suddenness and multitude of triggers, polyps can swell up and appear within a day in response to a variety of environmental factors. It is a chronic condition that can recur if the underlying irritation allergy or infection is not adequately controlled.