Bile is produced by the liver and is secreted into bile ducts, which drain into the gallbladder, where it is stored. Bile is a greenish fluid that is important for the digestion and absorption of cholesterol, fats and vitamins in food. Gallstones develop when the chemical composition of the bile is upset in some way. This occurs most commonly if the concentration of cholesterol in the bile is high or the liver fails to produce enough of the 'detergent' substances that normally keep cholesterol dissolved in the bile. Solid fragments of cholesterol can then form in the bile, which combine with bile pigments and other bile components to become gallstones.
Gallstones are extremely common, but cause no problems for most people.
The main danger comes from inflammation and infection when the bile system is obstructed. Gallstones do not usually cause any symptoms unless they block a duct or cause infection. It develops if drainage of the bile out of the liver is blocked sufficiently to cause bile to back up in the liver, so that its constituents spill over into the bloodstream. If the gallbladder itself is blocked by gallstones, it may become inflamed. The person has symptoms similar to those above, but the pain tends to be worse and more constant.