The term 'Hepatitis' refers to inflammation of the liver. Inflammation is the local reaction of the body, in this case the liver, in response to a damaging agent. It leads to accumulation of inflammatory cells, swelling of tissue and cells and eventually the death of cells. In case of chronic hepatitis, a compensatory response of the body may include the formation of scar tissue (fibrosis) and remodeling of the liver into nodules. The latter condition is called cirrhosis.

A number of different agents can cause hepatitis, including infective agents (virus, bacteria, other organisms), chemical poisons, drugs and alcohol or an immune response towards the organ itself (autoimmune hepatitis).

Viral hepatitis refers to a set of at least 5 viruses that are known to cause hepatitis: hepatitis A (HAV), hepatitis B (HBV), hepatitis C (HCV), hepatitis D (HDV), and hepatitis E (HEV). It is widely assumed that there are other, as yet unidentified, hepatitis viruses.

The most common types of viral hepatitis are hepatitis A, B, and hepatitis C and in some parts of the world hepatitis E . Both hepatitis B and C can lead to serious, permanent liver damage, and sometimes acute liver failure and death. Chronic persistence of the virus is a major cause of cirrhosis and death, as well as liver failure or liver cell cancer.

There are two primary modes of transmission of viral hepatitis: Water-food-borne and blood-borne. In the former case hepatitis A or E are implied which are spread through contaminated food and water. They do not cause chronic liver disease. By contrast, blood borne viral hepatitis, cause by the hepatitis B, C or D virus and may lead to long-term, persistent infections and chronic liver disease with potentially lethal consequences.