Biotin is a water-soluble B-complex vitamin that acts as a coenzyme in the metabolism of fats and amino acids. It plays a role in various metabolic reactions involved in cell growth, fatty acid synthesis, and protein synthesis. Biotin deficiency is rare in humans but can result from consuming large amounts of raw egg whites due to the avidin protein binding to biotin and preventing its absorption. Mild deficiency symptoms include dermatitis, hair loss, and fatigue.