Pellagra (which means "rough skin" from the Italian pelle agra) is due to a niacin deficiency or deficiency of the niacin precursor tryptophan. It is also referred to as mal del sole. Pellagra is a condition hallmarked by a symptom complex of the "4 Ds:" dermatitis (photosensitive rash), dementia, diarrhea, and death. The disease may be chronic with a relapsing-remitting course.

Pellagra is found worldwide but is more common in developing countries where poverty and malnutrition are more common (in part because the staple grains are not fortified with niacin). In addition to the skin, the neurologic system and gastrointestinal system are involved. Skin eruption tends to be photodistributed, symmetric, and erythematous. It may be accompanied by pain or itch. Various neurologic and gastrointestinal complaints such as dizziness, tremors, insomnia, fatigue, mood symptoms, nausea, vomiting, and diarrhea can be present and may precede skin manifestations.

The most common etiologies of pellagra are alcohol use disorder, various medications, inadequate intake, and malabsorption. Risk factors include poverty, staple diet that is poor in niacin (maize, Indian millet, or jowar), eating disorders, human immunodeficiency virus (HIV), alcohol abuse, medication (isoniazid, pyrazinamide, carbamazepine, carbidopa, chloramphenicol, phenytoin, phenobarbital), chemotherapy (5-fluorouracil, 6-mercaptopurine, azathioprine), post-surgical complications (gastrectomy), carcinoid syndrome (tryptophan is converted to serotonin instead of niacin), malabsorptive states (eg, Crohn disease, Hartnup disease), and hypothyroidism.

Symptoms of niacin or tryptophan deficiency take months to develop due to large tissue stores. Death due to multiorgan failure will occur in 4-5 years if left untreated.