Nasal polyps (NP) are benign lesions arising from the mucosa of the nasal sinuses (commonly at the outflow tract of one or more of the sinuses) or from the mucosa of the nasal cavity.

Source : Therapeutics and Clinical Risk Management. 4(2): 507–512.

Nasal polyps are common - perhaps affecting as much as 40% of the global population at some stage in their lives

The etiology of NP is unknown. Some theories consider polyps a consequence of conditions which cause chronic inflammation in the nose and nasal sinuses characterized by stromal edema and variable cellular infiltrate (Bateman et al 2003). While many aspects have been documented to support this theory, the initiating cause remains unknown and may be different in many cases.

[Source as above]

The polyps are known to be 'associated' with various diseases - such as Cystic Fibrosis and Asthmaplugin-autotooltip__plain plugin-autotooltip_bigAsthma

Asthma is a common, (and currently incurable) long term inflammatory disease of the airways of the lungs, characterized by variable and recurring symptoms such as reversible airflow obstruction, and bronchospasm. Episodes of asthma frequently feature wheezing, coughing, chest tightness, and shortness of breath.- and also with sensitivity to aspirin.

It's thought there are also links with fungal and bacterial infections, but no single cause has been found.