A gallstone is a small, hard lump that forms inside the gallbladder, a small organ near your liver that helps digest fatty foods. Think of it like a pebble forming inside your body, made from hardened digestive fluid.

Gallstones can be as tiny as a grain of sand or as large as a golf ball. Most people who have them don't even know it because gallstones often cause no problems at all. But sometimes a gallstone can block the tube that carries digestive fluid from the gallbladder, causing sudden, intense pain in the belly. When this happens, doctors might need to remove the gallstone or even the entire gallbladder with surgery.

While gallstones sound alarming, many people live their whole lives with them without ever needing treatment. Doctors typically only worry about gallstones if they start causing pain or other health problems.