Darkening of skin is one of the symptoms of primary biliary cholangitis... There is currently no known specific treatment for PBC. Vitamins A, D and K can be prescribed, usually when jaundice is present; cholestyramine and antihistamines can successfully relieve itching. Ursodeoxycholic acid, a bile salt, has been shown to improve liver function and delay the development of fibrosis..Consult dermatologist once for clinical examination if any other cause they will do the needful.