Short answer
Hepatitis B is a liver virus that spreads through sex, blood, and childbirth. With transmission mechanics worth understanding precisely because the protection (vaccination plus barriers) is nearly complete.
Many adult infections resolve on their own, but chronic infection can silently scar the liver toward cirrhosis and cancer, which is why testing and vaccination schedules exist.
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See Tests & Prices →Transmission routes, ranked by efficiency
Vaginal and anal sex (anal highest among sexual routes), sharing injection equipment, needlesticks, and birth to an infected mother.
It does not spread through food, water, hugging, or casual contact. Fear in those directions wastes worry that belongs on the real routes.
Condoms plus verified vaccination status end sexual transmission; sterile equipment discipline ends blood-borne transmission.
The broader route map is covered in How Do Sexually Transmitted Infections Spread?.
Symptoms and silent progression
Acute infection is often silent; when symptomatic: fatigue, nausea, abdominal pain, dark urine, and jaundice.
Chronic infection usually causes no symptoms for years while slowly damaging the liver. The silence that makes screening (not symptom-watching) the detection strategy for at-risk adults.
Testing and diagnosis without guesswork
Blood panels (surface antigen, surface antibody, core antibody, plus liver enzymes and viral load when indicated) distinguish susceptible, immune, acutely infected, and chronically infected states.
Interpretation needs a clinician. Single markers mislead, and panel patterns require trained reading.
How laboratory reports read generally is covered in How to Read a Laboratory STI Report.
Vaccination and prevention that works
The hepatitis B vaccine series is routine in childhood with catch-up for adults per schedules, plus birth dose for newborns.
Vaccinated household and sexual contacts of infected people should confirm immunity.
Condoms and never sharing injection equipment add protection.
Vaccine specifics live in What STI Vaccines Exist in the United States?.
Management principles, not prescriptions
Acute cases need monitoring and supportive care; chronic cases need specialist follow-up with periodic labs, imaging, and antivirals when clinical criteria are met.
Alcohol avoidance and liver-healthy habits matter throughout.
Treatment thresholds and drug choices belong to hepatology. Patients contribute adherence, attendance, and honesty about alcohol and exposures.
When to seek care
Get tested after possible exposure, if a partner is infected, or during pregnancy (screening is routine); seek urgent care for jaundice with confusion, bleeding, or severe illness.