Gallstones are lumps of sold material that form in the gallbladder.
In the UK, up to one in 10 adults have the condition. It affects around 15 per cent of people in the US.
Gallstones can resemble grains of sand or large pebbles.
They are formed from chemicals in bile and can consist of just cholesterol, a mixture of calcium and a pigment from red blood cells, or a combination of the two.
Gallstones have been linked to high-cholesterol diets, as well as liver damage and fasting.
Most people are unaware they have gallstones.
The most common symptom is abdominal pain, which can last up to eight hours and be severe.
This may be mistaken for a heart attack.
Pain occurs due to the gallbladder trying to expel the stones.
If gallstones have been discovered via a scan for something else and are not causing symptoms, they are often left without treatment.
Gallbladder inflammation may require antibiotics to be administered in hospital.
Severe symptoms may lead to people having the organ removed.
The gallbladder, which is involved in digestion, is not essential for life.
Source: British Liver Trust