How is HIV passed on?

To pass on the virus, infected body fluids (semen, vaginal fluids, anal mucous, breast milk, or blood) need to get into someone else's bloodstream. There are several ways HIV can be passed on.
HIV can be passed on by receiving blood transfusions or other blood-related products from an infected person, or donations of semen (artificial insemination), skin grafts and organ transplants.

Other factors that affect whether HIV is passed on

HIV isn't actually as infectious as many other sexually transmitted infections (STIs). It isn't automatically passed on every time a positive and a negative person have unprotected sex, for example.