Hepatitis B is a type of virus that can infect the liver.

Symptoms can include:

• feeling sick
• being sick
• lack of appetite
• flu-like symptoms, such as tiredness, general aches and pains, and headaches
• yellowing of the skin and eyes (jaundice)

However, many people don't realise they have been infected with the virus because the symptoms may not develop immediately, or even at all.

It takes between 40 and 160 days for any symptoms to develop after exposure to the virus.

Read more about the symptoms of hepatitis B.

How does hepatitis B spread?

Hepatitis B can be spread through blood and body fluids such as semen and vaginal fluids, so it can be caught:

• during unprotected sex, including anal and oral sex
• by sharing needles to inject drugs such as heroin

Hepatitis B in pregnancy

A mother can also pass on the hepatitis B infection to her newborn baby, but the infection can be prevented if the baby is vaccinated immediately after birth.

Read more about hepatitis B in pregnancy.

In England, people who are most at risk of contracting hepatitis B include:

• people who inject drugs
• people who change sexual partners frequently

Read more about the causes and risk factors for the hepatitis B infection.

How is it diagnosed?

Hepatitis B is diagnosed by a blood test that shows a positive reaction to hepatitis B surface antigen (the outer surface of the hepatitis B virus that triggers a response from your immune system).

A positive result means your liver is releasing hepatitis B protein into your blood, which suggests chronic infection.

Your GP may also request a liver function test. This is a blood test that measures certain enzymes and proteins in your bloodstream, which indicates whether your liver is damaged. It will often show raised levels if you are infected with the hepatitis B virus.

Stages of infection

In most cases, the hepatitis B virus will only stay in the body for around one to three months. This is known as acute hepatitis B.

In around 1 in 20 cases in adults, the virus will stay for six months or longer, usually without causing any noticeable symptoms. This is known as chronic hepatitis B.

Chronic hepatitis B is particularly common in babies and young children: 9 in 10 children infected at birth and around 1 in 5 children infected in early childhood will develop a long-term infection.

People with chronic hepatitis B can still pass the virus on to other people, even if it is not causing any symptoms.

Around 20% of people with chronic hepatitis B will go on to develop scarring of the liver (cirrhosis), which can take 10 to 20 years to develop, and around 1 in 10 people with cirrhosis will develop liver cancer.

Read more about complications of hepatitis B.

How is it treated?

There is currently no specific treatment for acute hepatitis B, other than using painkillers to relieve symptoms.

Treatment for chronic hepatitis B depends on how badly your liver is affected. It can be treated using medications designed to slow the production of the virus and prevent damage to the liver.

Read more about the treatment of hepatitis B.

Can it be prevented?

There is a vaccine thought to be 95% effective in preventing hepatitis B. Because of the relative rarity of hepatitis B in England, the vaccine is not given as part of the routine childhood vaccination schedule.

Vaccination would usually only be recommended for people in high-risk groups, such as:

• people who inject drugs or have a sexual partner who injects drugs
• people who change their sexual partner frequently
• people travelling to or from a part of the world where hepatitis B is widespread
• healthcare workers who may have come into contact with the virus

Pregnant women are offered screening for hepatitis B. If they are infected, their baby can be vaccinated shortly after birth to prevent them also becoming infected.

Read more about hepatitis B vaccination.

Who is affected?

Hepatitis B is uncommon in England and cases are largely confined to certain groups, such as drug users, men who have sex with men, and certain ethnic communities (for example, South Asian, African and Chinese). There were 5,478 newly reported cases in England during 2011.

In contrast, hepatitis B is common in other parts of the world, particularly east Asia and sub-Saharan Africa. The World Health Organization estimates that hepatitis B is responsible for 600,000 deaths a year worldwide.

Outlook

The vast majority of people infected with hepatitis B are able to fight off the virus and fully recover from the infection within a couple of months.

Most people with chronic hepatitis B have very little liver damage. A small minority of people go on to develop cirrhosis of the liver and, in some cases, liver cancer.

It's therefore important to get yourself vaccinated if you fall into one of the high-risk groups for catching hepatitis B.