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 aid digestion.
It's still unclear exactly what leads to this imbalance, but gallstones can form if:
- there are unusually high levels of cholesterol inside the gallbladder (about four in every five gallstones are made up of cholesterol)
- there are unusually high levels of a waste product called bilirubin inside the gallbladder (about one in every five gallstones is made up of bilirubin)
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 one stone will form, but there are often several at the same time.
Who’s at risk?
Gallstones are more common if you:
- are female, particularly if you've had children, are taking the combined Pill, or are undergoing high-dose oestrogen therapy
- are overweight or obese
- are aged 40 years or older (the older you are, the more likely you are to develop gallstones)
- have a condition that affects the flow of bile – such as cirrhosis (scarring of the liver), primary sclerosing cholangitis, or obstetric cholestasis
- have Crohn's disease or irritable bowel syndrome (IBS)
- have a close family member who's also had gallstones
- have recently lost weight (from either dieting or weight-loss surgery)
- are taking an antibiotic called ceftriaxone