A nasal polyp is a mass of swollen, mucus-covered tissue that grows out from the sinuses into the nasal passages inside the nose. One or more polyps may appear at the same time and block the nasal passages, making it difficult for a person to breathe and reducing the sense of smell.

Nasal polyps commonly develop in people who have chronic sinus infections.

Small polyps can usually be treated with nasal sprays containing corticosteroids. If polyps do not respond to treatment with a nasal spray, they may need to be removed surgically. But even when treated successfully, polyps frequently return.