Hepatitis is an inflammation or swelling of the liver that occurs when tissues of the liver become injured or infected. Inflammation can cause the liver to not work properly and, sometimes, can progress to other diseases. Hepatitis is usually caused by viral infection, though certain toxins, drugs, some diseases, excessive alcohol intake, and bacteria can also cause some forms of hepatitis. The five main types of hepatitis viruses are classified as A, B, C, D and E. Hepatitis C is a viral infection infecting the liver cells. It may present as a mild illness lasting a few weeks to a serious, lifelong illness that progressively damages the liver. Hepatitis C can be either 'acute' (short-term infection for less than 6 months) or 'chronic' (long-term infection). Hepatitis B and C have led to chronic disease in millions of people and, together, are the most common causes of liver cirrhosis and cancer. Vaccines are available to prevent hepatitis B, but there is no vaccine to prevent hepatitis C.