Gallstones are hard particles that form in the gallbladder. This is a small pouch that sits under the liver and that functions as a storage bag for bile. Bile is made in the liver, stored in the gallbladder and passes into the small intestine through the bile duct. The fluid, which is green and bitter tasting, contains emulsifiers that helps break down fats so they can be more easily digested.

It is common for some of the compounds in bile to become solid and hard. These particles are tiny at first, but they can then attract other particles and grow. Someone with gallstones may have just one large stone, or many smaller ones. The stones themselves contain cholesterol or calcium or bile pigments, or a mixture of two or three different compounds.Gallstones are very common. Around 10% of all adults have gallstones and the condition becomes more likely over the age of 40. But only a small proportion of people whose gallbladder contains gallstones experience problems. The most common sign that gallstones are becoming troublesome is biliary colic – pain in the upper right of the abdomen. Once any sort of symptoms develop, surgery to remove the gallbladder is the only effective treatment.

In the UK around 4.5 million people have gallstones at any one time and 50,000 of them need to have their gallbladder removed each year.