Biotin was first isolated from egg yolk in 1935 and is found in a wide variety of foods of animal and plant origin. In animals it is stored in the liver. Apart from the exogenous origin, a part of the biotin is produced by the bacteria of the intestinal flora. Chronic use of antibiotics and other drugs has been shown to affect the bacterial production of the vitamin. As a coenzyme, biotin is involved in the production of energy from the metabolism of carbohydrates and proteins as well as in the production of prostaglandins from the lipids of cell membranes. In addition, it contributes to the differentiation of keratinocytes in the skin, to the regulation of the hair cycle and to the normal function of the bone marrow.