Gallstones are hard particles that develop in the gallbladder, a small, pear-shaped organ located in the upper right abdomen, below the liver. Gallstones can range in size from a grain of sand to a golf ball. The gallbladder can develop a single large gallstone, hundreds of tiny stones, or both small and large stones. Gallstones can cause sudden pain in the upper right abdomen. This pain, called a gallbladder attack or biliary colic, occurs when gallstones block the ducts of the biliary tract.

What causes gallstones?
Imbalances in the substances that make up bile cause gallstones. Gallstones may form if bile contains too much cholesterol, too much bilirubin, or not enough bile salts. Scientists do not fully understand why these imbalances occur. Gallstones also may form if the gallbladder does not empty completely or often enough.

Who is at risk for gallstones?
Certain people have a higher risk of developing gallstones than others:

• Women are more likely to develop gallstones than men. Extra estrogen can increase cholesterol levels in bile and decrease gallbladder contractions, which may cause gallstones to form. Women may have extra estrogen due to pregnancy, hormone replacement therapy, or birth control pills.
• People over age 40 are more likely to develop gallstones than younger people.
• People with a family history of gallstones have a higher risk.
• American Indians have genetic factors that increase the amount of cholesterol in their bile. In fact, American Indians have the highest rate of gallstones in the United States—almost 65 percent of women and 30 percent of men have gallstones.
• Mexican Americans are at higher risk of developing gallstones.

Other factors that affect a person’s risk of gallstones include:

• Obesity. People who are obese, especially women, have increased risk of developing gallstones. Obesity increases the amount of cholesterol in bile, which can cause stone formation.
• Rapid weight loss. As the body breaks down fat during prolonged fasting and rapid weight loss, the liver secretes extra cholesterol into bile. Rapid weight loss can also prevent the gallbladder from emptying properly. Low-calorie diets and bariatric surgery—surgery that limits the amount of food a person can eat or digest—lead to rapid weight loss and increased risk of gallstones.
• Diet. Research suggests diets high in calories and refi­ned carbohydrates like white bread increase the risk of gallstones. Refi­ned carbohydrates are grains processed to remove bran and germ, which contain nutrients and ­fiber.
• Certain intestinal diseases. Diseases that affect normal absorption of nutrients, such as Crohn’s disease, are associated with gallstones.
• Metabolic syndrome, diabetes, and insulin resistance. These conditions increase the risk of gallstones. Metabolic syndrome also increases the risk of gallstone complications.
• Cirrhosis—a condition in which the liver slowly deteriorates and malfunctions due to chronic, or long lasting, injury.
• Infections in the bile ducts can lead to gallstones.
• Severe hemolytic anemias—conditions in which red blood cells are continuously broken down, such as sickle cell anemia.

What are the symptoms and complications of gallstones?
Many people with gallstones do not have symptoms. Gallstones that do not cause symptoms are called asymptomatic, or silent, gallstones. Silent gallstones do not interfere with the function of the gallbladder, liver, or pancreas.

If gallstones block the bile ducts, pressure increases in the gallbladder, causing a gallbladder attack. The pain usually lasts from 1 to several hours. Gallbladder attacks often follow heavy meals, and they usually occur in the evening or during the night.

Gallbladder attacks usually stop when gallstones move and no longer block the bile ducts. However, if any of the bile ducts remain blocked for more than a few hours, complications can occur. Complications include swelling of the gallbladder and severe damage or infection of the gallbladder, bile ducts, or liver.

A gallstone that becomes lodged in the common bile duct near the duodenum and blocks the pancreatic duct can cause inflammation of the pancreas.

Left untreated, blockages of the bile ducts or pancreatic duct can be fatal.

When should a person talk with a health care provider about gallstones?
People who think they have had a gallbladder attack should notify their health care provider. Although these attacks usually resolve as gallstones move, complications can develop if the bile ducts remain blocked.

People with any of the following symptoms during or after a gallbladder attack should see a health care provider immediately:

• Abdominal pain lasting more than 5 hours
• Nausea and vomiting
• Fever—even a low-grade fever—or chills
• Yellowish color of the skin or whites of the eyes, called jaundice
• Tea-colored urine and light-colored stools

These symptoms may be signs of serious infection or inflammation of the gallbladder, liver, or pancreas.