Causes

Scientists don't yet fully understand what causes nasal polyps, why some people develop long-term inflammation, or why irritation and swelling (inflammation) triggers polyps to form in some people and not in others. The swelling occurs in the fluid-producing lining (mucous membrane) of your nose and sinuses.

There's some evidence that people who develop polyps have different immune system responses and different chemical markers in their mucous membranes than do those who don't develop polyps.

Nasal polyps can form at any age, but they're most common in young and middle-aged adults.

Nasal polyps may form anywhere in your sinuses or nasal passages, but they appear most often in an area where sinuses near your eyes, nose and cheekbones all drain through winding passages into your nose.