Nasal polyps are often caused by irritation in the nose resulting from an allergy or infection that causes the nasal passages to become red and swollen with dripping fluid, explains Healthline. Nasal polyps form into a small cyst that can potentially block nasal passages.
Common triggers for nasal polyps include hay fever or allergic rhinitis, sensitivity to non-steroidal anti-inflammatory drugs, chronic sinus infections, asthma and medical conditions such as Churg-Strauss syndrome and cystic fibrosis, according to Healthline. Heredity can also play a role in the development of nasal polyps. Some people develop polyps in the nose for unknown reasons and may not have a history of sinus, allergy or nasal problems.