A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Biotin helps some enzymes break down substances in the body for energy and helps tissues develop. It is found in yeast, whole milk, egg yolks, and organ meats. Biotin is water-soluble (can dissolve in water) and must be taken in every day. Not enough biotin can cause skin, nerve, and eye disorders. Biotin is present in larger amounts in some cancer tissue than in normal tissue. Attaching biotin to substances used to treat some types of cancer helps them find cancer cells. Also called vitamin H.