Gallstones are formations of large particles, ranging from the size of a grain of sand to over a centimeter across, that form in the gall bladder. They precipitate from bile, an organic detergent produced by the liver, which assists the body to digest fat. For reasons that are not clear, in some patients either salts or fats precipitate out of the bile, forming particles which grow in the gall bladder until they are expelled through the bile duct. However, some stones become lodged in the bile duct, where the pressure continues to push on the stone until it is dislodged. However, if the stone is not dislodged, bacteria can travel up the bile duct to the gall bladder, causing it to become inflamed.