Pellagra is a disease that occurs when a person does not get enough niacin (one of the B complex vitamins) or tryptophan (an amino acid) in their diet. It can also occur if the body fails to absorb these nutrients.

The disease is common in certain parts of the world (in people consuming large quantities of corn). It is characterized by scaly skin sores, diarrhea, inflamed mucous membranes, and mental confusion and delusions. It may develop after gastrointestinal diseases or alcoholism.