AIDS is a chronic infectious disease caused by human immunodeficiency virus infection. The transmission of AIDS requires a variety of factors, first of all, there must be a source of infection, through a certain transmission route to cause infection of susceptible people. Since bodily fluids can contain a certain amount of virus, the transmission is caused by exposure to bodily fluids. Semen and vaginal secretions are both types of body fluids, but they contain different concentrations of virus. The concentration of virus in semen is higher than in vaginal secretions, so the chance of transmission from male to female is higher than that from female to male.