Hepatitis B is a viral infection that attacks the liver, caused by the hepatitis B virus (HBV). It can range from a short-lived illness that clears on its own to a lifelong chronic condition that raises the risk of liver failure and liver cancer. Globally, an estimated 254 million people live with chronic hepatitis B, making it one of the most common infectious diseases in the world.
How Hepatitis B Spreads
HBV spreads when blood, semen, or other body fluids from an infected person enter the body of someone who isn’t infected. Even microscopic amounts of blood can transmit the virus. The most common routes include:
- Birth: A mother with hepatitis B can pass the virus to her baby during delivery. This is the leading cause of new infections worldwide.
- Sexual contact: Unprotected sex with an infected partner is a major route of transmission in adults.
- Shared needles or syringes: Injecting drugs with shared equipment carries high risk.
- Needlestick injuries: Healthcare workers can be exposed through accidental skin punctures.
- Shared personal items: Razors, toothbrushes, or anything that might carry trace amounts of blood can transmit HBV.
Hepatitis B does not spread through casual contact like hugging, sharing food, coughing, or sneezing.
Symptoms and Timeline
After exposure, symptoms typically appear around 90 days later, though the range spans 60 to 150 days. Many adults with acute hepatitis B have no symptoms at all. When symptoms do show up, they can include:
- Fatigue and loss of appetite
- Nausea, vomiting, or abdominal pain
- Dark urine or pale, clay-colored stools
- Yellowing of the skin and eyes (jaundice)
- Joint pain
- Fever
These symptoms can be mild or severe enough to require hospitalization. In most healthy adults, the immune system clears the virus within a few weeks to months, and the person recovers fully with lasting immunity. The danger is when the infection doesn’t clear.
Acute vs. Chronic Infection
Hepatitis B comes in two forms. Acute infection is the initial phase, lasting up to several months. If the virus remains detectable in the blood for six months or longer, the infection is classified as chronic.
Your age at the time of infection is the single biggest factor in whether the virus becomes chronic. About 90% of infants infected at birth develop chronic hepatitis B because their immune systems are too immature to fight it off. Among children infected between ages 1 and 5, roughly 25 to 50% develop chronic infection. For healthy adults, the picture is much more favorable: over 95% clear the virus on their own during the acute phase.
Chronic hepatitis B often produces no symptoms for years or even decades. People can carry and spread the virus without knowing they’re infected, which is why screening matters so much.
Long-Term Risks of Chronic Infection
Left untreated, chronic hepatitis B slowly damages the liver over time. The two most serious complications are cirrhosis (permanent scarring that replaces healthy liver tissue) and liver cancer, specifically a type called hepatocellular carcinoma.
The lifetime risk of liver cancer for people with chronic hepatitis B is estimated at 27% for men and 8% for women. That risk climbs significantly when cirrhosis is already present: among people with cirrhosis, roughly 10 to 17% develop liver cancer within five years. The risk also scales with how actively the virus is replicating in the body, which is why monitoring viral levels is a key part of long-term care.
Not everyone with chronic hepatitis B faces these outcomes. Many people live with the virus for decades without developing serious liver disease, particularly if the infection is monitored and treated when necessary.
How Hepatitis B Is Diagnosed
Hepatitis B is diagnosed through blood tests that look for specific markers. Three are especially important:
- Surface antigen (HBsAg): A protein on the surface of the virus. If this is positive, you currently have an active hepatitis B infection, either acute or chronic.
- Surface antibody (anti-HBs): If this is the only marker present, you’re immune, either from vaccination or from recovering from a past infection.
- Core antibody (anti-HBc): This shows up in anyone who has ever been infected. Combined with the other two markers, it helps clarify whether the infection is current, resolved, or chronic.
If the surface antigen remains positive for six months or more, the infection is confirmed as chronic. At that point, additional testing measures how much virus is in the blood and how well the liver is functioning, which guides treatment decisions.
Treatment for Chronic Hepatitis B
There is currently no cure for chronic hepatitis B, but antiviral medications can suppress the virus effectively and dramatically reduce the risk of liver damage. Treatment works by blocking the virus from copying itself, which lowers viral levels in the blood and allows the liver to heal.
Most people who need treatment take a daily pill, typically for years and sometimes indefinitely. The goal isn’t to eliminate the virus entirely but to keep it suppressed at levels low enough that it stops harming the liver. Regular blood tests track viral levels and liver function to make sure treatment is working.
Not everyone with chronic hepatitis B needs immediate treatment. If the virus is in an inactive phase with low viral levels and no signs of liver damage, doctors may recommend monitoring with regular checkups rather than starting medication right away. Treatment is typically recommended when blood tests show active viral replication or evidence of liver inflammation.
Globally, treatment access remains a major gap. Only about 3% of people living with chronic hepatitis B, roughly 7 million people, had received antiviral therapy as of 2022. Just 13% had even been diagnosed.
Prevention and Vaccination
The hepatitis B vaccine is one of the most effective tools in preventing infection. It’s been available since the 1980s and is now part of the routine childhood immunization schedule in most countries.
For children and most adults, the standard vaccine series is three doses spread over several months. A newer two-dose option is available for adults 18 and older, making it easier to complete the series. After finishing the full series, the vaccine provides long-lasting protection for the vast majority of people.
Vaccination at birth is especially critical because of the high risk of mother-to-child transmission. In sub-Saharan Africa, which accounts for 63% of new hepatitis B infections globally, only 18% of newborns receive the birth dose. This gap is one of the main reasons the virus continues to spread in certain regions.
Global Burden
Hepatitis B remains a massive public health challenge. The 254 million people currently living with chronic infection are concentrated in specific parts of the world. Ten countries, including China, India, Nigeria, Indonesia, and Ethiopia, carry nearly two thirds of the global burden of hepatitis B and C combined. The Western Pacific region alone accounts for 47% of hepatitis B deaths.
Viral hepatitis, primarily hepatitis B and C together, claims approximately 3,500 lives every day worldwide, driven largely by complications that develop over years of untreated infection. Expanding vaccination, screening, and treatment access in heavily affected regions remains the clearest path to reducing those numbers.