Vitamin H, more commonly known as biotin, is part of the B complex group of vitamins. Your body needs biotin to metabolize carbohydrates, fats, and amino acids, the building blocks of protein. Biotin is often recommended for strengthening hair and nails, and it's found in many cosmetic products for hair and skin. It’s rare to be deficient in biotin. Symptoms include hair loss, dry scaly skin, cracking in the corners of the mouth (called cheilitis), swollen and painful tongue that is magenta in color (glossitis), dry eyes, loss of appetite, fatigue, insomnia, and depression. People who have been on parenteral nutrition -- nutrition given intravenously -- for a long period of time, those taking antiseizure medication or antibiotics long-term, and people with conditions like Crohn’s disease that make it hard to absorb nutrients, are more likely to be deficient in biotin. There are not many good quality studies evaluating biotin. Many of its proposed uses are based on weak evidence or case reports.