糙皮病又称癞皮病，是一种维生素缺乏性疾病，主要诱因是缺乏维生素B3（烟酸）和蛋白质，特别是含必需氨基酸色氨酸的蛋白质。色氨酸能被转化为烟酸，大约60mg色氨酸能被转化成1mg烟酸，过程中需要维生素B₁、B₂和B₆的参与。因此色氨酸含量丰富但不含烟酸的食物，比如牛奶也能有效预防糙皮病。然而，如果通过食物摄入的色氨酸全部被用于蛋白质合成，则仍有可能引起糙皮病。

糙皮病是一种地区性流行病，主要发生于非洲，墨西哥，印度尼西亚以及中国。在输出型社会中，糙皮病患者一般是贫穷、酗酒的无家可归者或者是拒绝进食的精神病患者。

Pellagra is a vitamin deficiency disease most frequently caused by a chronic lack of niacin (vitamin B₃ or synonym: vitamin PP (from: Pellagra Preventing factor)) in the diet. It can be caused by decreased intake of niacin or tryptophan, and possibly by excessive intake of leucine. It may also result from alterations in protein metabolism in disorders such as carcinoid syndrome or Hartnup disease. A deficiency of the amino acid lysine can lead to a deficiency of niacin, as well.