Hepatitis B is a viral infection affecting the liver that can range from a short-term illness to a lifelong condition, potentially leading to serious complications if left unmonitored. Understanding this infection, its transmission routes, and available prevention methods can help protect you and your loved ones from its effects.

Epidemiology

Hepatitis B represents one of the most significant liver health challenges facing the world today. According to the World Health Organization, approximately 254 million people were living with chronic hepatitis B infection in 2022, with around 1.2 million new infections occurring each year.^[1] This makes hepatitis B the most common liver infection worldwide.^[2]

In the United States, the situation appears more contained but still concerning. The Centers for Disease Control and Prevention estimates that roughly 640,000 adults in the US have chronic hepatitis B, while approximately 14,000 people experience acute hepatitis B infections.^[1] However, a particularly troubling aspect of this infection is that about one in two people with hepatitis B do not know they are infected, which increases the risk of unknowingly spreading the virus to others.^[1]

The burden of hepatitis B varies dramatically across different regions and populations. The infection is most prevalent in the WHO Western Pacific Region and the WHO African Region, where 97 million and 65 million people respectively live with chronic infection.^[1] In the South-East Asia Region, 61 million people are infected, while the Eastern Mediterranean, European, and Americas regions have 15 million, 11 million, and 5 million cases respectively.^[1]

Within the United States, hepatitis B does not affect all populations equally. In 2023, rates of acute hepatitis B were highest among non-Hispanic Black people, with the highest rates observed in states in or near the Appalachian region.^[1] For chronic hepatitis B, the pattern differs significantly. The highest rate of newly reported chronic cases in 2023 was among non-Hispanic Asian and Pacific Islander people, with rates 9.9 times higher than those among non-Hispanic White people.^[1] This disparity reflects both geographic patterns of infection in countries where these populations originate and differences in screening and diagnosis rates.

Age also plays an important role in hepatitis B patterns. In 2023, 48% of all acute hepatitis B cases occurred in people aged 40 to 59 years.^[1] This age distribution reflects the complex interplay of risk factors, exposure opportunities, and the time it takes for infections to be detected and reported.

The global health impact of hepatitis B is substantial. In 2022, hepatitis B resulted in an estimated 1.1 million deaths worldwide, primarily from complications such as cirrhosis (severe scarring of the liver) and hepatocellular carcinoma (primary liver cancer).^[1] These deaths occur despite the availability of effective vaccines and treatments, highlighting the ongoing need for better diagnosis, linkage to care, and public health interventions.

Causes

Hepatitis B is caused by infection with the hepatitis B virus, commonly abbreviated as HBV. This virus specifically targets the liver, where it establishes infection and can cause inflammation and damage to liver cells over time.^[1] The virus itself is remarkably infectious and can survive on surfaces for at least seven days, meaning that even dried blood or other body fluids can potentially transmit infection if they come into contact with broken skin or mucous membranes.^[3]

The hepatitis B virus is classified in the Hepadnaviridae family and measures between 40 and 42 nanometers when complete with its protective envelope.^[3] Inside this envelope sits the viral genetic material, which is a circular, partially double-stranded DNA genome. After a person is exposed to the virus, it enters the bloodstream and travels to the liver, which becomes the primary site where the virus replicates and produces more copies of itself.^[3]

What makes hepatitis B particularly challenging to eliminate from the body is how the virus operates once inside liver cells. The virus creates a special form of its genetic material called covalently closed circular DNA (or cccDNA), which remains stable inside the nucleus of liver cells and serves as a template for producing more virus.^[4] This persistent form of viral DNA is why current treatments can suppress the virus but cannot yet provide a complete cure.

Risk Factors

While anyone can contract hepatitis B, certain circumstances, behaviors, and life situations significantly increase a person’s risk of exposure to the virus. Understanding these risk factors helps identify who should be screened and who may benefit most from vaccination.

One of the most significant risk factors relates to where a person was born. Individuals born in countries where hepatitis B is common face higher risk, particularly those from certain regions in Asia, South America, Africa, the Middle East, and the Caribbean.^[5] People born in the United States whose parents came from countries with high hepatitis B rates also face increased risk, even if they themselves were born in the US.^[3]

Family connections to someone with hepatitis B create risk as well. Living in the same household with someone who has chronic hepatitis B increases exposure risk through shared items that might contact blood, such as razors or toothbrushes, though the virus does not spread through casual contact like hugging, sharing eating utensils, or coughing and sneezing.^[2]

Sexual activity represents another important transmission route. Having multiple sexual partners, engaging in unprotected sex, or being a man who has sex with men all increase the risk of hepatitis B infection.^[3] People with a history of sexually transmitted infections also face elevated risk.^[5]

People who inject drugs face particularly high risk due to potential needle sharing. Any sharing or reuse of needles, syringes, or other drug injection equipment can transmit the virus, whether this occurs in healthcare settings, in the community, or among people who use drugs.^[1] Even microscopic amounts of infected blood remaining on equipment can cause infection.

Certain medical conditions and treatments also increase risk. People receiving dialysis for kidney disease, those taking immunosuppressant medications (drugs that weaken the immune system to prevent organ rejection after transplantation or to treat autoimmune conditions), and individuals with HIV or hepatitis C infections all face higher risk.^[2] Healthcare and public safety workers who may be exposed to blood on the job also have increased risk of infection.^[3]

People who have spent time in jail or prison face elevated risk, as do those who have received tattoos or body piercings, particularly if performed with unsterilized equipment.^[2] Blood transfusions received before widespread screening of the blood supply also posed risk, though modern blood screening has made this route of transmission very rare in countries with developed healthcare systems.

Infants born to mothers with hepatitis B face extremely high risk of infection during birth, which is why all pregnant women should be screened for hepatitis B and why newborns of infected mothers receive both vaccine and protective antibodies immediately after birth.^[5]

Symptoms

One of the most challenging aspects of hepatitis B is that many people infected with the virus experience no symptoms at all, particularly in the early stages of infection. This silent nature of the disease means people can be infected for months or even years without knowing it, potentially spreading the virus to others during this time.^[1]

When symptoms do occur, they typically appear between one and four months after a person has been exposed to the virus, though they can emerge as early as two weeks after infection.^[2] The average time between exposure and symptom development, called the incubation period, is about 60 days, with a range of 40 to 90 days being common.^[3]

The symptoms of acute hepatitis B, when they appear, can range from very mild to quite severe. Common symptoms include pain in the stomach area, often described as a dull ache or discomfort in the upper right side where the liver is located.^[2] Many people experience significant fatigue and weakness that goes beyond normal tiredness, making even routine activities feel exhausting.

Digestive symptoms frequently accompany hepatitis B infection. Loss of appetite is common, sometimes accompanied by nausea, stomach pain, and vomiting.^[1] These symptoms can make eating difficult and may lead to unintended weight loss.

Fever and joint pain may occur, making the infection feel similar to influenza.^[2] This flu-like presentation is one reason why hepatitis B infections sometimes go unrecognized initially, as people may assume they simply have a viral illness that will resolve on its own.

Changes in the appearance of urine and stool provide important visual clues to liver involvement. Urine may become dark in color, appearing brown or tea-colored, while stools may become pale, light-colored, or clay-colored.^[1] These changes occur because the infected liver cannot process certain substances normally.

Jaundice, a yellowing of the skin and the whites of the eyes, is one of the more recognizable symptoms of hepatitis B when it occurs. This yellowing happens because bilirubin, a yellow pigment normally processed by the liver, builds up in the body when the liver is inflamed or damaged.^[2] The visibility of jaundice can vary depending on a person’s natural skin tone, making it easier to see in some individuals than others.

Some people may develop swelling from fluid accumulation in the belly, arms, or legs, which indicates more significant liver problems.^[2] This symptom is more common in people who have progressed to chronic hepatitis B with liver damage.

For acute hepatitis B infections, symptoms typically last for a few weeks, though some people may feel sick for up to six months.^[2] The severity can vary widely from person to person. Some individuals experience only mild illness requiring just rest at home, while others develop severe symptoms requiring hospitalization.^[5]

Most people with chronic hepatitis B have no symptoms for many years or even decades after infection, which is why this form of the disease is particularly dangerous.^[1] Symptoms may not appear until significant liver damage has occurred, sometimes only becoming noticeable when complications like cirrhosis or liver cancer develop. This is why regular monitoring by a healthcare provider is crucial for anyone known to have chronic hepatitis B, even if they feel completely well.

Prevention

The most effective way to prevent hepatitis B infection is through vaccination. The hepatitis B vaccine is safe, widely available, and remarkably effective, offering nearly 100% protection against the virus when the complete series is administered.^[1] The vaccine works by training the immune system to recognize and fight off the hepatitis B virus if the body encounters it in the future, without causing actual infection.

Vaccination schedules vary depending on age, but the vaccine typically involves a series of shots given over several months. For infants, the first dose is ideally given within 24 hours of birth, with additional doses following at specific intervals in the first year of life.^[1] This early vaccination is particularly important because infants and young children who become infected are at highest risk of developing chronic hepatitis B infection that lasts throughout their lives.

The Centers for Disease Control and Prevention recommends hepatitis B vaccination for nearly everyone. All infants should receive the vaccine, as should children and adolescents up to age 18 who did not receive it as infants.^[1] Adults between ages 19 and 59 who have not been vaccinated should also receive the vaccine. For adults age 60 and older, vaccination is recommended for those at higher risk, though anyone in this age group can choose to receive the vaccine even without specific risk factors.^[5]

It’s important to complete the entire vaccine series to ensure full protection. If someone starts the series but misses their second or third dose on schedule, they do not need to start over – they can simply continue the series where they left off.^[6] However, protection is not complete until all doses in the series have been received.

Beyond vaccination, several behavioral and practical measures can help prevent hepatitis B transmission. Because the virus spreads through contact with infected blood and body fluids, avoiding exposure to these materials is key. Never sharing needles, syringes, or other drug injection equipment eliminates one major route of transmission.^[1]

Using barrier protection during sexual activity, particularly condoms, significantly reduces the risk of sexual transmission.^[7] People with multiple sexual partners or those whose partners have hepatitis B should be especially careful about protection and should consider vaccination if not already vaccinated.

In healthcare and public safety settings, following proper infection control procedures, including using gloves when contact with blood or body fluids is possible, helps protect workers from exposure.^[3] Healthcare facilities should have clear protocols for handling needlestick injuries and other exposures.

Personal care items that might come into contact with blood, such as razors, toothbrushes, nail clippers, and even jewelry used for body piercings, should not be shared between household members.^[7] If getting tattoos or body piercings, ensuring that the establishment uses proper sterilization techniques and new needles for each client reduces transmission risk.

For people who have been exposed to hepatitis B but are not yet infected, post-exposure treatment called prophylaxis may prevent infection if given quickly enough. This treatment may include the hepatitis B vaccine and, in certain circumstances, an injection of hepatitis B immune globulin (HBIG), which provides immediate but temporary protection while the vaccine begins to work.^[8] This treatment is most effective when given within 24 hours of exposure, though it may still help if given within a few days.

Pregnant women with hepatitis B can take steps to protect their babies. All pregnant women should be tested for hepatitis B at their first prenatal visit.^[5] If a mother tests positive, her newborn should receive both the hepatitis B vaccine and HBIG within 12 hours of birth, which dramatically reduces the risk of transmission from mother to baby.

People with chronic hepatitis B should also get vaccinated against hepatitis A, another virus that attacks the liver, to prevent additional liver damage from a second infection.^[9] Protecting the liver from multiple sources of harm is an important part of staying healthy with hepatitis B.

Pathophysiology

Understanding what happens in the body when hepatitis B virus causes infection helps explain why this disease can be so challenging to manage and why it affects people so differently.

When the hepatitis B virus enters the body, it travels through the bloodstream to reach the liver. The virus has a special ability to recognize and attach to liver cells, called hepatocytes, using a specific entry point on the cell surface called the sodium taurocholate cotransporting polypeptide.^[4] This explains why the virus specifically targets the liver rather than other organs.

Once inside a liver cell, the virus sheds its outer envelope and moves its genetic material into the cell’s nucleus, which is the control center where DNA is normally stored. Inside the nucleus, the virus repairs and completes its partially formed DNA, creating a stable circular form called covalently closed circular DNA.^[4] This DNA form becomes bound to the proteins that normally package human DNA, allowing it to persist inside liver cells for very long periods, potentially for the entire life of that cell.

The liver cell then reads the instructions from this viral DNA and uses them to produce new virus particles. The virus uses a unique replication strategy involving reverse transcription, meaning it copies its DNA into RNA and then back into DNA again, similar to how HIV replicates.^[2] This complex replication process produces large numbers of new virus particles that are released from the infected liver cell and can go on to infect other liver cells.

The damage to the liver in hepatitis B infection does not come directly from the virus destroying liver cells. Instead, most of the liver damage results from the body’s own immune response trying to eliminate the virus.^[8] When the immune system recognizes that liver cells are infected, it sends specialized cells to attack and destroy those infected cells. This immune attack causes inflammation in the liver, which over time can lead to scarring.

The balance between the virus and the immune response determines whether someone clears the infection or develops chronic hepatitis B. Most adults who get infected have strong immune responses that successfully eliminate the virus, leading to recovery.^[3] Approximately 95% of infected adults recover completely from acute HBV infection and do not develop chronic infection.

However, when infection occurs in infants or young children, their developing immune systems often cannot mount an effective response to clear the virus. About 90% of infected infants and 30% of children infected between ages 1 and 5 will remain chronically infected.^[3] In these cases, the virus establishes a long-term presence in the liver.

Chronic hepatitis B infection typically progresses through several distinct phases. In the early phase, called immune tolerance, the virus replicates actively but the immune system does not attack infected liver cells, so there is little liver damage.^[10] Later, the immune system may begin fighting the virus more actively, leading to an immune clearance phase where liver inflammation and damage increase. In some people, the immune system eventually gains control of the virus, entering an immune control phase where viral replication is suppressed and liver damage slows or stops. However, the virus can sometimes escape from immune control later, leading to renewed liver inflammation and damage.^[10]

When chronic inflammation continues for years or decades, the constant cycle of liver cell damage and repair leads to the formation of scar tissue, a process called fibrosis.^[2] As fibrosis progresses, it can advance to cirrhosis, where extensive scarring disrupts the normal structure of the liver and impairs its ability to function properly. Severely damaged liver tissue also has an increased risk of developing cancer, specifically hepatocellular carcinoma.

The hepatitis B virus can also remain in the body in a largely inactive form even after someone appears to have cleared the infection. The stable covalently closed circular DNA can persist in liver cell nuclei without causing active infection or symptoms, but it can potentially reactivate if a person later takes immunosuppressant medications that weaken the immune system’s ability to keep the virus in check.^[2] This is why people with evidence of past hepatitis B infection need monitoring if they begin treatments that suppress immunity.

In rare cases, acute hepatitis B can cause such severe and rapid liver damage that the liver loses most of its function very quickly, a dangerous condition called acute liver failure or fulminant hepatitis.^[8] This life-threatening complication requires immediate intensive medical care and may necessitate liver transplantation for survival. Fortunately, this severe outcome is uncommon, but it represents the most serious immediate danger from acute hepatitis B infection.