HIV can be transmitted from an infected person to another through:
Blood (including menstrual blood)
Semen
Vaginal secretions
Breast milk
Blood contains the highest concentration of the virus, followed closely by semen, followed by vaginal fluids. These are the three basic fluids that infect adults with HIV.
The risk from these fluids can be worsened or lessened depending on how they get into someone else's body, which we will discuss below.
Breast milk can contain a high concentration of the virus, but in this situation, transmissibility depends on who and how. An adult can ingest a small amount of breast milk at minimal risk. But an infant, with its very small body and newly forming immune system, consumes vast quantities of breast milk relative to its body weight. Therefore an infant is at risk from breast milk, whereas an adult probably is not.