<unk>  is a disease caused by a lack of the vitamin niacin (vitamin B3). Symptoms include inflamed skin, diarrhea, dementia, and sores in the mouth. Areas of the skin exposed to either sunlight or friction are typically affected first. Over time affected skin may become darker, stiffen, peel, or bleed. There are two main types of<unk> , primary and secondary. Primary<unk>  is due to a diet that does not contain enough niacin and tryptophan. Secondary<unk>  is due to a poor ability to use the niacin within the diet. This can occur as a result of alcoholism, long-term diarrhea, carcinoid syndrome, Hartnup disease, and a number of medications such as isoniazid. Diagnosis is typically based on symptoms and may be assisted by urine testing. Treatment is with either niacin or nicotinamide supplementation. Improvements typically begin within a couple of days. General improvements in diet are also frequently recommended. Decreasing sun exposure via sunscreen and proper clothing is important while the skin heals. Without treatment death may occur. The disease occurs most commonly in the developing world, specifically sub-Saharan Africa.
Pellagra
Pemphigus
Koilonychia
Kwashiorkor
Melanonychia
Porphyria
Crepitus
Photodermatitis