HIV is passed through blood, semen and vaginal fluid. If infected blood, semen or vaginal fluid gets into your body, the virus might infect you too. Most people with AIDS became infected from having sex or sharing drug needles with a person who has HIV. The virus also can be passed from a mother to her baby during pregnancy or at birth. HIV is NOT spread through skin-to-skin contact.
In the past, HIV sometimes was spread to people who received infected blood through transfusions. But as of March 1985, all blood supplies are screened for HIV.
Many people who have HIV don’t know it, because they look and feel fine for many years after they become infected. This means that they can pass the virus to others through sex or shared needles without knowing it.