Hepatitis B is an infectious liver disease. It is caused by the hepatitis B virus (HBV). Infections of hepatitis B occur only if the virus is able to enter the bloodstream and reach the liver. Once in the liver, the virus reproduces and releases large numbers of new viruses into the bloodstream. Hepatitis B is a vaccine-preventable bloodborne infection. Hepatitis means inflammation of the liver. There are many causes of hepatitis. For example, drinking too much alcohol, various drugs and chemicals, and also several different germs (viruses) can cause hepatitis. One virus that causes hepatitis is called the hepatitis B virus. This leaflet is only about hepatitis B. See separate leaflets called Hepatitis A and Hepatitis C, which are caused by different viruses. Hepatitis B is a virus that is carried from the bloodstream to the liver. It can then affect and damage your liver. Hepatitis B is a contagious liver disease that results from infection with the Hepatitis B virus. When first infected, a person can develop an “acute” infection, which can range in severity from a very mild illness with few or no symptoms to a serious condition requiring hospitalization. Acute Hepatitis B refers to the first 6 months after someone is exposed to the Hepatitis B virus. Some people are able to fight the infection and clear the virus. For others, the infection remains and leads to a “chronic,” or lifelong, illness. Chronic Hepatitis B refers to the illness that occurs when the Hepatitis B virus remains in a person’s body. Over time, the infection can cause serious health problems. Hepatitis B is highly infectious. An estimated 700,000 to 1.4 million people in the United States have the virus, and most of them acquired it in childhood.