Mucus is a thick, slippery and usually clear substance that is
produced in the lining of body cavities or canals, such as the nose, throat,
sinuses, and airways of the lungs. Mucus protects and moistens the lining of
body organs, such as the stomach and intestines, and traps dust particles,
smoke, bacteria, and other irritants that enter the nose when a person
inhales.
Mucus that becomes too thick and sticky can block the airway or
digestive system or cause other problems in the body. Thick and sticky mucus
is difficult for the body to remove and can increase the risk of
infection.