Cholic acid is a major primary bile acid produced in the liver and is usually conjugated with glycine or taurine. It facilitates fat absorption and cholesterol excretion. Bile acids are steroid acids found predominantly in the bile of mammals. The distinction between different bile acids is minute, and depends only on the presence or absence of hydroxyl groups on positions 3, 7, and 12. Bile acids are physiological detergents that facilitate excretion, absorption, and transport of fats and sterols in the intestine and liver. Bile acids are also steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine, and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH, and consequently require a carrier for transport across the membranes of the enterohepatic tissues. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. Bile acids have potent toxic properties (e.g. membrane disruption) and there are a plethora of mechanisms to limit their accumulation in blood and tissues. When present in sufficiently high levels, cholic acid can act as a hepatotoxin and a metabotoxin. A hepatotoxin causes damage to the liver or liver cells. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Among the primary bile acids, cholic acid is considered to be the least hepatotoxic while deoxycholic acid is the most hepatoxic. The liver toxicity of bile acids appears to be due to their ability to peroxidate lipids and to lyse liver cells. Chronically high levels of cholic acid are associated with familial hypercholanemia. In hypercholanemia, bile acids, including cholic acid, are elevated in the blood. This disease causes liver damage, extensive itching, poor fat absorption, and can lead to rickets due to lack of calcium in bones. The deficiency of normal bile acids in the intestines results in a deficiency of vitamin K, which also adversely affects clotting of the blood. The bile acid ursodiol (ursodeoxycholic acid) can improve symptoms associated with familial hypercholanemia.