Gallstones are small pebble-like stones made of material that precipitated out of bile, a digestive fluid. Merck Manuals, an online medical library, reports that gallstones are more common in women than men. They are also more common in older people, and 20 percent of people in United States over the age of 65 have gallstones. Small gallstones cause few problems, but larger gallstones may get stuck in the gall bladder or the bile duct, which can cause intense pain. There are three main types of gallstones: cholesterol, pigment and mixed.
Cholesterol
The National Digestive Diseases Information Clearinghouse, or NDDIC, is a service of the National Institutes of Health, and reports that 80 percent of gallstones are made of cholesterol. Being overweight greatly increases a person's risk of developing cholesterol gallstones, according to NDDIC, because being overweight reduces the amount of bile salts and increases the amount of cholesterol in the bile. The excess cholesterol can precipitate out of the bile and form gallstones.
Cholesterol stones are also more common in people with diets that are high in fat and cholesterol. This elevates the concentration of cholesterol in bile. Merck Manuals adds that most cholesterol gall stones form in the gallbladder.
Pigment
The NDDIC describes pigment gallstones as stones that are very dark in color and made of bilirubin, another normal component of bile. Scientists know less about the cause of pigment gallstones than of cholesterol gallstones, according to Oxford Surgical and Bariatric Clinic, a clinic that performs the surgical removal of gallstones. What is known is that pigment gallstones develop more often in people who have blood disorders, liver cirrhosis and bile duct infections. All of these conditions can result in bile that is more concentrated in bilirubin than normal. According to Merck Manuals, the exact color of the stone can provide information about the location of stone formation. Black pigment stones develop in the gallbladder, and brown pigment stones form in the bile ducts.
Mixed
Oxford Surgical and Bariatric Clinic notes that a mixed gallstone is composed of both cholesterol and various salts that are present in the bile. The risk factors that make cholesterol gallstones more likely to develop, such as being overweight, also increase the risk of mixed gallstones developing, due to the fact that cholesterol is one component of this type of stone.
