Hepatitis B is caused by a virus (the hepatitis B virus, or HBV) that infects the liver and is spread from person to person through blood and certain body fluids such as semen and vaginal fluids. It does not come from food, water, or casual contact like hugging, coughing, or sharing utensils.
How the virus spreads
The virus “comes from” other infected people and is passed on when their blood or body fluids get into another person’s bloodstream. Common routes include unprotected sex, sharing needles or injection equipment, and unsafe medical, tattoo, or piercing procedures with unsterilized instruments.
Another major source is transmission from an infected mother to her baby during birth, which is a leading cause of chronic hepatitis B in parts of the world where the virus is very common. Children can also become infected in early life through close contact with infected blood or body fluids in the household.
Geographic and historical origin
HBV has been infecting humans for thousands of years, and viral DNA has been found in ancient human remains from many regions, showing it is a very old human infection. Modern genetic studies suggest that current human hepatitis B strains likely diversified thousands of years ago, with some evidence pointing to early origins in regions such as North Africa and the Middle East before spreading globally with human migration.
Key points to remember
- Hepatitis B always comes from another infected person; it is not created spontaneously in the body.
- Transmission happens when infected blood or certain body fluids enter another person, especially through sex, needles, or childbirth.
- A safe and effective vaccine can prevent infection and is widely recommended, especially for infants and people at higher risk.
