Gallstones are crystal-like masses that typically form in the gallbladder. The gallbladder is a small organ located on the right side of the abdomen, just below the liver. The gallbladder's main function is to store bile (made by the liver) and secrete it into the small intestine to help with digestion. Bile is made of water, cholesterol, fats, bile salts (natural detergents that break up fat), and a pigment called bilirubin. Gallstones form if the bile contains too much cholesterol, bile salts, or bilirubin.
There are two types of gallstones. Cholesterol stones contain mostly hardened cholesterol and account for approximately 80% of gallstones. Pigment stones are made of bilirubin and account for the other 20%. Gallstones can range in size from very small to as large as a golf ball. The gallbladder may develop any number and size of stones.
Gallstones are more common in women and people who are older, as well as in certain groups of people, such as Indigenous populations and people who are overweight. In Canada, 20% of women and 10% of men over the age of 60 have gallstones, but many never experience symptoms. However, complications from gallstones can be serious if symptomatic stones are left untreated.