Hepatitis B is an infection of the liver caused by the hepatitis B virus.
It can cause inflammation (swelling) of the liver, and sometimes significant liver damage.
Many people do not even realise they have been infected with the virus, because the typical flu-like symptoms may not develop immediately, or even at all.
You can become infected with hepatitis B if you are not immune (resistant) to the virus and have been exposed to the blood or body fluids of an infected person (see below).
A vaccine is available to protect against hepatitis B.
How do you catch it?
The hepatitis B virus is present in body fluids such as blood, saliva, semen and vaginal fluid. It can be passed from person to person through unprotected sex (without using a condom) or by sharing needles to inject drugs, for example.
Hepatitis B is 100 times more infectious than HIV.
Infected mothers can also pass the virus to their baby during childbirth, often without knowing they are infected.
The incubation period (the time it takes from coming into contact with the virus to developing infection) is between one and six months.
Chronic illness
In some people, the hepatitis B virus will go on to cause a chronic (long-term) illness, where it lasts for longer than six months. This is very common in babies and young children, but it can also occur in 2–10% of infected adults.
If you develop chronic hepatitis B, you may not have symptoms and you could pass on the virus without realising you are infected.
If you do have symptoms, these may come and go. You could develop serious liver damage (see Symptoms).
How common is it?
Hepatitis B is not very common in the UK: approximately one in 1,000 people are thought to have the virus.
However, in some inner-city areas with a high percentage of people from parts of the world where the virus is common, as many as one in 50 pregnant women may be infected.
Worldwide, the occurrence of hepatitis B is highest in sub-Saharan Africa, south-east Asia and the Pacific islands, such as the Hawaiian islands, the Solomon islands and Fiji.
The lowest incidence of hepatitis B is found in Australia, New Zealand, northern and western Europe and North America. There are approximately 350 million carriers of the virus around the world.
Outlook
The vast majority of people who are infected with hepatitis B are able to fight off the virus and fully recover from the infection within a couple of months.
However, most babies infected with hepatitis B have a poorer outlook, as their infection usually becomes chronic.
