Hepatitis B is caused by a virus which attacks and damages the liver.Children who have the disease usually develop a very mild illness and sometimes they have no sign of illness at all. The illness itself is more serious for adults.On rare occasions, people don't clear the virus from their blood and continue to carry the virus. Many years later liver damage and liver cancer may develop.
Hepatitis B is passed on through close contact with blood and other body fluids from an infected person, eg, from cuts and scratches, sharing toothbrushes, and sex without a condom. Hepatitis B can also be passed on from pregnant women to their babies, usually at birth. If you have hepatitis B, you are infectious for several weeks before signs appear until weeks or months later. Some people are infectious for years.