Nasal polyps are soft, painless, noncancerous growths lining the nose or sinuses that often occur in groups. The exact cause of nasal polyps is not fully understood, but research suggests that they are linked to chronic rhinosinusitis, which is inflammation of the nasal passages and sinuses lasting 12 weeks or more. The development of nasal polyps is associated with long-term swelling and inflammation in the nose from allergies, asthma, or infection. Researchers believe that allergies and infections cause the inflammation, which features swelling, redness, and fluid buildup. They think that because they’ve studied tissue taken from nasal polyps, which contained extra eosinophils, white blood cells linked to infections and allergic reactions. Small growths filled with fluid can turn into polyps as they grow. Some of the risk factors for nasal polyps include asthma, aspirin sensitivity, chronic sinus infections, cystic fibrosis, and hay fever (allergic rhinitis) .