Hepatitis B virus is the pathogen that causes hepatitis B. It usually infects humans quietly through blood, body fluids and mother-to-child transmission. In healthy adults, due to sound immune function, the hepatitis B virus will be cleared by the body’s immune system soon after infection or only acute hepatitis will occur and be cured; infants, young children, teenagers, and middle-aged and elderly people with poor immunity, as the immune function cannot deal with the invasive hepatitis B virus, the virus infection is often latent for a long time, it is easy to form chronic hepatitis B virus carriers; with the age of However, most of the hepatitis B virus infected people just carry the virus for life without developing the disease, but their blood and body fluids (such as: saliva, sweat night) still have a certain degree of infectiousness.