In primary sclerosing cholangitis (PSC), the bile ducts (a type of passageway) inside and outside the liver become narrowed due to inflammation and scarring. As the scarring increases, the ducts become narrowed or blocked. The ducts are important 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 remain in the liver and damage liver cells. In addition, fat and vitamins A, D, E and K may not be well absorbed. Eventually, primary sclerosing cholangitis can cause liver failure.

Approximately one out of every 100,000 individuals in the world is diagnosed with primary sclerosing cholangitis.