A compact mass of hair that forms in the alimentary canal (especially in the stomach of animals as a result of licking fur), notably of cats: A trichobezoar is a concretion within the stomach or intestines formed of hairs, also known as a "hairball" or "hair ball".

A bezoar is a ball of swallowed foreign material (usually hair or fiber) that collects in the stomach and fails to pass through the intestines.

Chewing on or eating hair or fuzzy materials (or indigestible materials such as plastic bags) can lead to the formation of a bezoar. The incidence is very low and the risk is greater among mentally retarded or emotionally disturbed children. Generally bezoars are seen in females (approximately 90%) aged 10 to 19.

The bezoar may need to be surgically removed (especially trichobezoars which tend to be large). Sometimes small bezoars can be removed through a scope placed through the mouth and into the stomach (similar to an EGD procedure). Then, follow the prevention measures described.