Nasal polyps are associated with irritation and swelling (inflammation) of the lining of your nasal passages and sinuses that lasts more than 12 weeks (chronic sinusitis).

However, it's possible to have chronic sinusitis without nasal polyps.

Nasal polyps themselves are soft and lack sensation, so if they're small, you may not be aware you have them. Multiple growths or a large polyp may block your nasal passages and sinuses.

Common signs and symptoms of chronic sinusitis with nasal polyps include:

• A runny nose
• Persistent stuffiness
• Postnasal drip
• Decreased or absent sense of smell
• Loss of sense of taste
• Facial pain or headache
• Pain in your upper teeth
• A sense of pressure over your forehead and face
• Snoring
• Frequent nosebleeds

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.

Any condition that triggers long-term irritation and swelling (inflammation) in your nasal passages or sinuses, such as infections or allergies, may increase your risk of developing nasal polyps.

Conditions often associated with nasal polyps include:

• Asthma, a disease that causes the airway to swell (inflame) and narrow
• Aspirin sensitivity
• Allergic fungal sinusitis, an allergy to airborne fungi
• Cystic fibrosis, a genetic disorder that results in abnormally thick, sticky fluids in the body, including thick mucus from nasal and sinus linings
• Churg-Strauss syndrome (eosinophilic granulomatosis with polyangiitis), a rare disease that causes the inflammation of blood vessels
• Vitamin D deficiency, which occurs when your body doesn't have enough vitamin D

Nasal polyps can cause complications because they block normal airflow and fluid drainage, and also because of the long-term irritation and swelling (inflammation) underlying their development.

Potential complications include:

• Obstructive sleep apnea. This is a potentially serious condition in which you stop and start breathing frequently during sleep.
• Asthma flare-ups. Chronic sinusitis can worsen asthma.
• Sinus infections. Nasal polyps can make you more susceptible to sinus infections that recur often.