Hepatitis B infection occurs when liver cells become infected with the hepatitis B virus (HBV). HBV is a virus that is transmitted in blood and other body fluids such as semen, vaginal secretions, or saliva. Some of the main routes of transmission include unprotected oral, vaginal, or anal sex and sharing intravenous needles with an infected person. Health care workers can contract the disease through an accidental stick with a needle used on a patient with HBV. Finally, pregnant women who have HBV may pass the disease to their babies during delivery. There is no risk of contracting HBV through casual contact such as hugging or shaking hands with someone who is infected.

The liver is a large abdominal organ with many critical functions including detoxifying chemicals, storing vitamins, processing nutrients absorbed in the small intestine, and producing bile to aid fat digestion. HBV infection of the liver can cause damage that disrupts the many body processes the liver is involved in and also causes a buildup of the bile precursor bilirubin, which turns the skin yellow (jaundice).