The paranasal sinuses are the air cavities that open into the nose. If the soft tissue lining of the sinuses becomes swollen, it fills the available space and can then expand into the nose forming a growth called a polyp. As there are a number of small sinuses between the eye and the nose, when polyps do occur, there will usually be several of them. The cause of nasal polyps is not well understood. Some believe that they result from an allergy to things in the atmosphere, while others believe that they are caused by a sinus infection .
Polyps block the nose.
Large polyps can prevent nasal breathing, forcing the individual to breathe through their mouth. They also cause reduced sense of smell. Occasionally they swell so much that they emerge from the nostril. If you have a severely blocked nose, you should see your doctor. Inspection of the nose will reveal the presence of polyps.