Gallstones are thought to be caused by an imbalance in the chemical make-up of bile inside the gallbladder. Bile is a liquid produced by the liver to help digestion.

It's unclear what causes the chemical imbalance, but gallstones can form if there are unusually high levels of:

These chemical imbalances cause tiny crystals to develop in the bile.

These can gradually grow (often over many years) into solid stones that can be as small as a grain of sand or as large as a pebble.

Sometimes only 1 stone will form, but there are often several at the same time.

Who's at risk

Gallstones are more common if you:

Page last reviewed: 1 August 2019
Next review due: 1 August 2019