Bile is stored in the gallbladder, a small pear-shaped sac underneath the liver, until it is needed for digestion. Gallstones can measure up to 1 inch. Sometimes a single gallstone forms, but there can be up to 10 or more. Gallstones become more common as you get older. They are two to three times more common in women than in men.
Gallstones build up from chemicals in the bile, usually cholesterol.
Gallstones develop when something happens to upset the balance of chemicals in the bile. For example, there may be too much cholesterol. Small, solid particles form, which clump together and gradually form a gallstone. Fasting can help gallstones to form, because if bile is not needed to digest food, it can become concentrated and stagnant in the gallbladder. Gallstones only cause problems in about one in five of the people that have them.