Primary sclerosing cholangitis (PSC) is a chronic liver disease that affects the bile ducts inside and outside the liver. It is a progressive condition that causes inflammation and scarring of the bile ducts, leading to narrowing and blockage. This disrupts the normal flow of bile, which is essential for digestion and removing waste products from the liver. Over time, PSC can cause serious liver damage, leading to liver failure or the need for a liver transplant.