Pellagra is a nutritional disease whose major manifestations are primarily due to the deficiency of nicotinic acid or its precursor tryptophan. Nicotinic acid, with an official name niacin, is a B-complex vitamin; and the amino acid tryptophan is its precursor.

Clinical manifestations of pellagra involve the symptoms of 4 Ds: dermatitis, diarrhea, dementia, and death. In pellagrins (patients with pellagra), skin lesions resemble burned areas and hence become much more painful when exposed to sunlight. Although the skin lesions occur most often on exposed areas of the body (such as face, neck, forearms, and lower legs), stomatitis (inflammation of mouth) involving a swelling and reddening of the tongue is as common. Diarrhea is usually the result of gastrointestinal disturbances. In severe cases, neurological change could occur leading to serious disorientation and dementia. In the old days, fatal cases were quite common.

Historically, pellagra was not recognized until around 1720, after the introduction of corn (maize) as a food commodity. There was supposition that as far back as during the pre-Columbian New World times, some pellagra-like incidents were experienced by people in Egypt and India living on Sorghum vulgare. Yet according to Roe (1973), author of the book A Plague of Corn - The Social History of Pellagra, no real evidence was available to support such a contention. There was documentation, however, showing that pellagra was first observed in the Asturia in Europe in 1735, by a Spanish physician named Don Gaspar Casal. At that time, pellagra was referred to as Mal de la Rosa.