What causes gallstones?

The two types of gallstones are cholesterol stones and pigment stones:

- Cholesterol stones - Bile contains water, cholesterol, fats, bile salts, and bilirubin. Bile salts break up fat, and bilirubin gives bile and stool a brownish colour. If the liquid bile contains too much cholesterol, too much bilirubin, or not enough bile salts, or when the gallbladder does not empty, as it should for some other reason, it can promote cholesterol stone forming. Cholesterol stones are usually yellow-green and are made primarily of hardened cholesterol. They account for about 80 percent of gallstones.

- Pigment stones - The cause of pigment stones is uncertain. They tend to develop in people who have cirrhosis, biliary tract infections, and hereditary blood disorders, such as sickle cell anaemia. Pigment stones are small, dark stones made of bilirubin.

Gallstones can be as small as a grain of sand or as large as a golf ball. The gallbladder can develop just one large stone, hundreds of tiny stones, or almost any combination.

The gallbladder and the ducts that carry bile and other digestive enzymes from the liver, gallbladder, and pancreas to the small intestine are called the biliary system.

Gallstones can block the normal flow of bile if they lodge in any of the ducts that carry bile from the liver to the small intestine. That includes the hepatic ducts, which carry bile out of the liver; the cystic duct, which takes bile to and from the gallbladder; and the common bile duct, which takes bile from the cystic and hepatic ducts to the small intestine.

Bile trapped in these ducts can cause inflammation in the gallbladder, the ducts, or, rarely, the liver. Other ducts open into the common bile duct, including the pancreatic duct, which carries digestive enzymes out of the pancreas.

If a gallstone blocks the opening to that duct, digestive enzymes can become trapped in the pancreas and cause an extremely painful inflammation called pancreatitis.

If any of these ducts remain blocked for a significant period of time, severe - possibly fatal - damage can occur, affecting the gallbladder, liver, or pancreas. Warning signs of a serious problem are fever, jaundice, and persistent abdominal pain.