In primary sclerosing cholangitis (PSC), the bile ducts (a type of passage) inside and outside the liver narrow. This is due to inflammation and scarring. As the scarring increases, the ducts become narrowed or blocked. The ducts are vital because they carry bile out of the liver.

Bile is a liquid that removes toxins from the body and helps break down fat in food. If the ducts are narrowed or blocked, toxins in bile stay in the liver and damage liver cells. Also fat and vitamins A, D, E and K may not be well absorbed. Over time, PSC can cause liver failure.

Around one out of every 100,000 people in the world are diagnosed with PSC.