The exact mechanism whereby the body’s own immune system attacks the liver is not yet known. It appears that certain types of white blood cells (the type of blood cell that usually fights infection), in addition to attacking foreign substances (e.g. germs and viruses) misread liver cells as foreign substances and start attacking these cells. The type of damage that follows is known as chronic hepatitis. A number of other conditions can cause identical patterns of liver damage. These include viruses such as hepatitis B and hepatitis C, certain types of drugs, and overload of certain metals such as copper and iron in the liver. There are also much rarer causes of chronic active hepatitis.