Hepatitis B: how it spreads, how it is tested and how to prevent it

Hepatitis B is a serious but largely preventable liver infection. Because many people have no symptoms, it can go unnoticed for years. This article explains how hepatitis B spreads, how it is detected, how it is managed and how it can be prevented, using the World Health Organization (WHO), the NHS and the US Centers for Disease Control and Prevention (CDC).

1. Introduction

Hepatitis B is a viral infection of the liver. It can be acute, a short-term illness that starts within 6 months of exposure, or chronic, a long-term infection that can last for life ^[3]. WHO estimates that 240 million people lived with chronic hepatitis B in 2024, with about 0.9 million new infections each year, and that the infection caused about 1.1 million deaths, mostly from cirrhosis (severe liver scarring) and liver cancer ^[1].

WHO says the hepatitis B vaccine gives almost complete protection against the virus ^[1].

2. How it spreads

The virus passes through blood, semen and certain other body fluids from an infected person entering another person's body, even in microscopic amounts ^[3]. WHO says that in areas where the infection is very common, the most usual routes are mother-to-child transmission at birth and spread between young children, especially through open cuts and sores. Other routes include needlestick injuries, tattooing, piercing, and sharing or reusing contaminated needles or sharp objects. Sexual spread is more common among unvaccinated people with several partners ^[1].

The NHS lists similar routes, including sharing needles, unsterilised equipment for tattoos, piercings or medical and dental procedures, and blood transfusions in countries that do not screen blood ^[2].

The CDC says hepatitis B is not spread through kissing, sharing utensils, sneezing, coughing, hugging, breastfeeding, or food or water ^[3].

Age at infection matters. WHO reports that infection in adulthood leads to chronic hepatitis in under 5 in 100 cases, whereas infection in infancy or early childhood leads to chronic infection in about 95 in 100 cases ^[1]. That is why vaccinating babies at birth is so important.

3. Signs and symptoms

Most newly infected people have no symptoms, or only mild ones ^{[1, 2]}. When symptoms occur they may include ^{[1, 2, 3]}:

• Tiredness and fever
• Nausea, vomiting and loss of appetite
• Pain in the upper tummy and joint pain
• Dark urine and pale or clay-coloured stools
• Jaundice, which is yellowing of the skin and the whites of the eyes

Acute symptoms often appear about 90 days after exposure ^[3]. Chronic infection usually causes no symptoms until decades later, and the NHS says an infection lasting longer than 6 months is called chronic ^{[2, 3]}.

4. Diagnosis and tests

Symptoms alone cannot tell hepatitis B from other types of viral hepatitis, so a laboratory blood test is needed. Blood tests confirm the infection, show whether it is acute or chronic and help assess how serious it is. A physical exam, an ultrasound scan and a test called elastography, which measures liver stiffness, can assess scarring ^[1].

The CDC recommends that all adults have a blood test for hepatitis B at least once in their lifetime. Testing is advised more often for pregnant women in every pregnancy, for babies born to women with hepatitis B, and for people with ongoing risk of exposure ^[3]. WHO notes that in 2024 only 27 in 100 people living with hepatitis B knew they had it ^[1].

5. Treatment and management

WHO says there is no specific treatment for acute hepatitis B. Care focuses on comfort, a suitable diet and fluids ^[1]. The NHS says acute infection usually clears without specific treatment, and a doctor may refer you to a liver specialist to check how your liver is working ^[2].

Chronic hepatitis B has no known cure, but it can be managed ^{[2, 3]}. WHO explains that oral antiviral medicines can slow cirrhosis, reduce the risk of liver cancer and improve long-term survival, and that most people who start treatment need to continue it for life ^[1]. Your specialist decides whether you need medicine and which one.

The CDC advises people with a new diagnosis to find a doctor who specialises in infectious, digestive or liver diseases, to have regular liver tests, to limit alcohol and to check with a doctor before taking any prescription, herbal, supplement or over-the-counter product ^[3]. The NHS also advises rest, plenty of fluids and avoiding sharing razors, toothbrushes or needles ^[2].

6. Prevention

Vaccination is the best way to prevent hepatitis B ^[3]. WHO recommends that all babies receive the first dose within 24 hours of birth, followed by two or three more doses at least four weeks apart. Protection lasts at least 20 years and probably for life, and boosters are usually not needed after the full series ^[1].

The CDC recommends vaccination for all infants, for all unvaccinated children and teenagers under 19, for adults aged 19 to 59 and for older adults at higher risk. Full protection needs the whole series ^[3].

Other protective steps listed by WHO and the NHS include using condoms, not sharing needles or piercing and tattoo equipment, and vaccination of health-care workers ^{[1, 2]}.

7. Special groups

Pregnant women can pass the virus to their baby at birth. WHO says preventing this relies on the baby's vaccine, sometimes given together with antiviral medicine, as decided by doctors ^[1]. The NHS says babies born to infected mothers get extra vaccine doses ^[2]. People living with HIV, health-care workers, people who inject drugs and partners or family members of an infected person are also named as groups for whom testing and vaccination matter ^{[1, 2]}.

8. When to see a doctor

The NHS advises seeing a doctor if you think you might have hepatitis B or are at higher risk of getting it ^[2]. Ask about a blood test and about vaccination, particularly if you have not been vaccinated.

Yellow skin or eyes, very dark urine, clay-coloured stools and severe tiredness can be symptoms of hepatitis B ^[3], so get medical advice promptly if you notice them. In an emergency, call your local emergency number (112 in India, 911 in the United States).

9. Conclusion

Hepatitis B is a common viral liver infection that often causes no symptoms but can lead to cirrhosis and liver cancer if it becomes chronic. A laboratory blood test is needed to confirm it. Specialist care can slow liver damage in chronic infection, and vaccination remains the most effective protection.