Hepatitis B is an infection caused by the hepatitis B virus (HBV), which causes inflammation and enlargement of the liver. HBV infections can vary from a mild form that lasts a few weeks to a chronic form that can cause lasting liver damage. HBV is spread through contact with blood or other body fluids from an infected person. Exposure can occur through sharing needles or through unprotected sex. People who live in or travel to areas where HBV is prevalent are at greater risk. It is possible for pregnant women to pass the infection to their babies, usually during or after birth.