Hepatitis B: what it is, transmission, testing, treatment and vaccine

Hepatitis B is a liver infection caused by a virus (HBV) that spreads through blood, through sex and from mother to baby at birth. Most adults clear it on their own within a few months. When it becomes long-term (chronic) it usually cannot be cured, but it can be controlled with antiviral medicines. A highly effective vaccine prevents it.

What hepatitis B is

The hepatitis B virus infects the liver and causes inflammation. It can lead to two types of infection:

• Acute: the first few months after infection. In adults, the body clears the virus in more than 95% of cases, and the person is then protected for life.
• Chronic: when the virus stays in the body for more than six months. The younger someone is when infected, the more likely this is: it happens in around 90% of babies infected at birth and in fewer than 5% of adults.

It is very widespread. According to the World Health Organization (WHO), around 240 million people were living with chronic hepatitis B in 2024, and it caused about 1.1 million deaths, mostly from cirrhosis and liver cancer.

Symptoms and when they appear

Many people notice nothing, especially young children. When symptoms do appear, they usually start 6 weeks to 6 months after infection (about 3 months on average):

• severe tiredness and loss of appetite;
• feeling or being sick, or pain in the upper right of the tummy;
• fever and joint pain;
• dark urine, pale poo and jaundice (yellow skin and eyes).

Chronic hepatitis B can go unnoticed for many years while it damages the liver. That is why testing matters even if you feel well.

How it is passed on, and how it is not

The virus is found in blood, semen and vaginal fluids, and it is very infectious. It spreads through:

• Sex: vaginal, anal or oral sex without protection with someone who has the virus. Anal sex carries a higher risk (see our guide to safe anal sex).
• Blood: sharing needles, syringes or other injecting equipment, or tattoos and piercings done with unsterilised equipment.
• Personal items that may carry traces of blood, such as razors or toothbrushes.
• Mother to baby during birth. Worldwide, this is one of the main routes.

Hepatitis B is not passed on by hugging, coughing or sneezing, sharing food, drinks or cutlery, or everyday contact. People with hepatitis B can work, study and live with others as normal.

Testing: when and how

Hepatitis B is diagnosed with a blood test. It looks for parts of the virus and for the body's antibodies. This shows whether the infection is recent or chronic, or whether you are protected by vaccination or a past infection. If it is chronic, liver blood tests follow, and sometimes an ultrasound or elastography scan (a painless test that measures liver stiffness).

After a possible exposure, the test may not pick up the virus in the first few weeks. Your clinician will tell you when to repeat it, usually after one to three months. Testing is also recommended in pregnancy, if you have another STI, if you have shared injecting equipment, or if your partner has hepatitis B. See how often to have an STI test.

Treatment: cure or control

Acute hepatitis B has no specific treatment. Rest, eating well, drinking fluids, avoiding alcohol and regular check-ups are advised while the body clears the virus. Most adults recover within one to three months.

Chronic hepatitis B usually cannot be cured, but it can be controlled. Not everyone needs medicine straight away: a liver specialist decides based on how the liver is doing. When needed, antiviral medicines keep the virus in check and greatly lower the risk of cirrhosis and liver cancer. They are often taken for many years or for life. That is why follow-up matters: according to the US CDC, people with chronic hepatitis B have a 15 to 25% risk of dying early from these complications.

You can still have sex. What matters is that your partners get tested and vaccinated, and that you use condoms until their protection is confirmed.

Pregnancy and newborns

Hepatitis B testing is offered at the first antenatal appointment. If the mother has the virus, the baby is given the vaccine and an antibody injection (immunoglobulin) within hours of birth, which protect them very effectively. Sometimes the mother also takes antiviral medicine late in pregnancy. Find out more in our pregnancy and postpartum guide.

Prevention: the vaccine and other steps

• Vaccine: it is safe and gives almost 100% protection, for at least 20 years and probably for life. It is given in several doses and is part of routine baby vaccinations in the UK and most countries. If you are an adult and not vaccinated, ask for it, especially if you have several partners, have HIV or work in healthcare.
• After a risky exposure if you are not vaccinated: get medical help as soon as possible, ideally within 24 hours. The vaccine, and immunoglobulin if needed, can prevent infection.
• Condoms for vaginal, anal and oral sex.
• Not sharing needles, razors or toothbrushes, and only getting tattoos and piercings with sterile equipment.

When to get help

Get help as soon as possible if you have had a risky exposure and are not vaccinated. Book an appointment if you have jaundice, dark urine or unexplained severe tiredness, if your partner has hepatitis B, or if you have never been tested and may have been at risk. If you have chronic hepatitis B, keep going to your check-ups, even when you feel well.