Biotin is a water-soluble B vitamin that is also known as vitamin H and coenzyme R. It is known to support healthy skin, hair, and nails, improve nervous system function, and promote a healthy metabolism and gastrointestinal tract. Biotin deficiencies can cause alopecia (hair loss), conjunctivitis, dermatitis, and neurological symptoms including depression, lethargy, and numbness and tingling of the extremities.