A sulfur-containing member of the vitamin B complex, 5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid, found in liver, egg yolk, milk and yeast, essential to the activity of multiple enzyme systems.
"She added an extra serving of egg yolks to her breakfast because she suspected that a deficiency in biotin might be causing her hair to thin out."