Hepatitis is inflammation of the liver. Six forms of Hepatitis are now recognized. These are labeled as Hepatitis A,B,C,D,E & F. Some forms of Hepatitis are sudden and brief (acute) while others are long lasting (chronic). Most forms of hepatitis are caused by viruses. The viruses have names similar to those of the diseases they cause. Hepatitis A, for example, is caused by the hepatitis A virus (HAV). Hepatitis B is caused by the hepatitis B virus (HBV), and so on.

The exact mechanism by which viruses cause hepatitis is not entirely understood. It appears that the disease is not caused by the virus itself, but by the body's immune system. When a foreign invader enters the body, the immune system begins to respond. It produces chemicals designed to kill the invader. These chemicals are called antibodies. The presence of antibodies in the bloodstream may have other effects on the body, including inflammation, swelling, and other symptoms. It appears that the liver becomes inflamed because of the antibodies produced by the immune system, not because of the virus itself.