Mucous Membrane
The moist lining of body cavities and passages that open to the outside.
What it means
Mucous membranes line the passages of the body that communicate with the exterior — the mouth, nose, airways, gut, and urinary and genital tracts.
They secrete mucus, which traps particles and organisms, keeps surfaces moist, and forms part of the body's first line of defence.
A spelling distinction worth knowing: mucous is the adjective describing the membrane; mucus is the noun for the fluid it produces.
In practice
"Mucosa" is the usual term in endoscopy and pathology reports — gastric mucosa, bowel mucosa, nasal mucosa — with descriptions of inflammation, ulceration or atrophy.
Because mucous membranes are thin and richly supplied with blood, they are also an efficient route for absorbing certain medicines.
Why it matters
Mucosal surfaces are the entry point for most infections, including sexually transmitted ones, which is why barrier protection reduces transmission.
Persistent mucosal ulceration — in the mouth, genitals or bowel — lasting more than three weeks warrants assessment.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026