It is thought that nasal polyps occur as a result of the inflammation (swelling) in the lining of the nasal cavities and sinuses, called the mucus membrane.
Inflammation causes fluid to build up in the cells of the mucus membrane. Over time, gravity pulls on the fluid-filled cells and causes them to develop into polyps.
Exactly what triggers the process of inflammation inside the nasal cavities is unclear. However, several theories have been suggested including:
- The inflammation is a response to a bacterial, viral or fungal infection.
- The inflammation is an allergic-like reaction, for example to pollution.
- Certain genes that a person inherits from their parents make them more likely to develop nasal polyps.
- Problems with the nervous system disrupt the normal flow of fluid through the lining of the nose, leading to inflammation.
- The immune system (the body’s natural defence against illness and infection) goes wrong in some way and begins to attack the tissues of the lining of the nose, causing it to become inflamed.
It's possible that a combination of these factors could be responsible for nasal polyps.
Risk factors
While the exact causes of nasal polyps are unknown, several factors increase your risk of developing them. These include:
- asthma that starts in adulthood - 20-40% of people with nasal polyps also have asthma
- allergic rhinitis - where a person develops cold-like symptoms due to an allergic reaction
- cystic fibrosis - where the lungs and digestive system become clogged with a sticky fluid (about 25% people with cystic fibrosis develop nasal polyps)
- having an intolerance to aspirin
- Churg-Strauss syndrome - a rare condition that causes inflammation of the blood vessels
