Your gallbladder is a small organ below the liver in the upper right abdomen. It’s a pouch that stores bile, a green-yellow liquid that helps with digestion. Most gallstones form when there’s too much cholesterol in the bile.
According to Harvard Health Publications, 80 percent of gallstones are made of cholesterol. The other 20 percent of gallstones are made of calcium salts and bilirubin.
It’s not known exactly what causes gallstones to form, though there are some theories.
Too much cholesterol in your bile
Having too much cholesterol in your bile can lead to yellow cholesterol stones. These hard stones may develop if your liver makes more cholesterol than your bile can dissolve.
Too much bilirubin in your bile
Bilirubin is a chemical produced when your liver destroys old red blood cells. Some conditions, such as liver damage and certain blood disorders, cause your liver to produce more bilirubin than it should. Pigment gallstones form when your gallbladder can’t break down the excess bilirubin. These hard stones are often dark brown or black.
Concentrated bile due to a full gallbladder
Your gallbladder needs to empty its bile to be healthy and to function properly. If it fails to empty its bile content, the bile becomes overly concentrated, which causes stones to form.