Hepatitis B spreads through blood and body fluids

Hepatitis B is a virus that lives in blood and certain body fluids. You get it when infected blood or fluids enter your bloodstream or mucous membranes — the moist linings inside your mouth, nose, eyes, or genitals. The virus does not spread through saliva alone, food, water, coughing, sneezing, or casual contact like shaking hands.

The three main routes of transmission are sexual contact with an infected person, sharing needles or injection equipment, and from mother to baby during pregnancy or birth. A smaller number of cases come from accidental needle sticks in healthcare settings or from sharing personal items that can cause tiny cuts or sores — like razors or toothbrushes — though this is less common than the three main routes.

Key Takeaways

  • Hepatitis B spreads through blood-to-blood contact, sexual contact, or from mother to baby at birth — not through saliva, food, or casual contact.
  • Sharing needles for drugs, steroids, or tattoos is one of the most common ways adults catch hepatitis B in developed countries.
  • Sexual transmission can happen with or without visible sores, and risk is higher if either partner has other sexually transmitted infections.
  • A hepatitis B vaccine prevents infection in about 95 percent of people who receive the full series and is part of routine childhood immunizations.
  • Babies born to infected mothers can be protected with vaccine and immunoglobulin shots given within hours of birth.

Sexual contact as a transmission route

Hepatitis B spreads during sexual contact because the virus can enter through tiny breaks in the skin or mucous membranes of the penis, vagina, rectum, or mouth. You do not need visible sores or bleeding for transmission to happen. The risk is higher if either partner has another sexually transmitted infection, because those infections can cause inflammation that makes the lining more permeable.

Condoms reduce but do not eliminate the risk, because the virus can be present on areas of skin the condom does not cover. People with multiple sexual partners, men who have sex with men, and sex workers face higher risk. Testing and vaccination before exposure are the most reliable ways to prevent infection through sexual contact.

Needle and injection equipment sharing

Sharing needles, syringes, or other injection equipment is how hepatitis B spreads most commonly among people who inject drugs. Even a tiny amount of infected blood left on a needle can carry enough virus to infect the next person who uses it. The same risk applies to needles used for steroids, hormones, or other non-medical injections.

Tattoo and piercing needles that are not properly sterilized can also transmit the virus, though regulated tattoo shops in developed countries use single-use needles or proper autoclaves. Sharing equipment for snorting drugs (like straws or rolled bills) carries lower risk than injection but is not risk-free if there are cuts or sores inside the nose.

Mother-to-baby transmission during pregnancy and birth

A pregnant woman with hepatitis B can pass the virus to her baby during pregnancy or, more commonly, during labor and delivery. The risk is highest during birth, when the baby may come into contact with infected blood and fluids. Babies infected at birth have a 90 percent chance of developing chronic hepatitis B, compared to about 5 percent of adults who are infected.

Hospitals screen pregnant women for hepatitis B as part of routine prenatal care. If a woman is infected, her baby receives hepatitis B vaccine and hepatitis B immunoglobulin (a shot of antibodies) within 12 hours of birth. This combination is about 95 percent effective at preventing infection. The baby then completes the vaccine series over the first six months of life.

Healthcare worker exposure and accidental needle sticks

Healthcare workers can catch hepatitis B from accidental needle sticks or cuts with contaminated instruments. The risk from a single needle stick is roughly 1 in 300, which is lower than some other bloodborne viruses but still significant. Workers in emergency departments, operating rooms, and dialysis centers face higher exposure risk.

Healthcare facilities have protocols to reduce this risk: using safety-engineered needles, proper hand hygiene, and immediate wound care after exposure. Healthcare workers are routinely vaccinated against hepatitis B before they begin work. If an unvaccinated worker has a needle stick exposure, they can receive hepatitis B immunoglobulin and begin the vaccine series within 24 hours to prevent infection.

Sharing personal items that cause cuts or sores

Hepatitis B can spread if you share items that break the skin or mucous membranes and come into contact with infected blood. Razors, toothbrushes, nail clippers, and other sharp personal items pose a risk if both people have cuts, sores, or bleeding gums. This route is much less common than sexual contact or needle sharing, but it is a real possibility in households where someone has hepatitis B.

The virus does not survive long outside the body, and it cannot pass through intact skin. Sharing drinking glasses, utensils, food, or towels with someone who has hepatitis B does not transmit the virus. Kissing is safe unless both people have open sores or bleeding in the mouth, which is rare.

Who is at higher risk for hepatitis B

Certain groups face higher risk of hepatitis B exposure based on their circumstances or behaviors. People who inject drugs, men who have sex with men, sex workers and their clients, and people with multiple sexual partners all have elevated risk. Healthcare workers, people with HIV or hepatitis C, and people in correctional facilities also face higher exposure risk.

People born in countries where hepatitis B is common (parts of Africa, Asia, and the Pacific) have higher rates of infection. Infants and children in these regions are at risk from mother-to-baby transmission and from exposure in their communities. Immigrants from these regions and their children may benefit from testing and vaccination even if they were not vaccinated in their birth country.

Frequently Asked Questions

Can you get hepatitis B from sharing a toothbrush?

Only if both people have bleeding gums or open sores in the mouth and the infected person's blood gets into the other person's mouth. This is possible but uncommon. The virus does not spread through saliva alone. If someone in your household has hepatitis B, using separate toothbrushes is a reasonable precaution, but casual contact and shared meals are safe.

Is hepatitis B spread through kissing?

Not through saliva. Kissing is safe unless both people have open sores or bleeding in the mouth, which is rare. Hepatitis B virus is not present in saliva in amounts that can cause infection. You cannot catch hepatitis B from kissing someone on the cheek or lips if there are no open wounds.

What should you do if you think you were exposed to hepatitis B?

Contact a doctor or urgent care clinic as soon as possible — ideally within 24 hours. They can test you and, if you are not already vaccinated, give you hepatitis B immunoglobulin and start the vaccine series. Post-exposure prevention is most effective when started quickly. Tell the doctor how you think you were exposed so they can assess your risk accurately.

Can you get hepatitis B from a blood transfusion?

The risk is extremely low in developed countries because blood banks screen all donated blood for hepatitis B. In countries with less rigorous screening, the risk is higher. If you received a transfusion before the 1990s, when screening became standard, your doctor may recommend testing.

Do you need the hepatitis B vaccine if you already had the infection?

If you had acute hepatitis B and recovered, you have lifelong immunity and do not need the vaccine. If you have chronic hepatitis B, the vaccine is not effective because your immune system is already infected. Talk to your doctor about whether testing is right for you based on your specific situation.