HIV transmission can occur when blood, semen (cum), pre-seminal fluid (pre-cum), vaginal fluid, or breast milk from an infected person enters the body of an uninfected person.

HIV can enter the body through a vein (e.g., injection drug use), the lining of the anus or rectum, the lining of the vagina and/or cervix, the opening to the penis, the mouth, other mucous membranes (e.g., eyes or inside of the nose), or cuts and sores. Intact, healthy skin is an excellent barrier against HIV and other viruses and bacteria.

These are the most common ways that HIV is transmitted from one person to another:

• by having sex (anal, vaginal, or oral) with an HIV-infected person;
• by sharing needles or injection equipment with an injection drug user who is infected with HIV; or
• from HIV-infected women to their babies before or during birth, or through breast-feeding after birth.

HIV also can be transmitted through receipt of infected blood or blood clotting factors. However, since 1985, all donated blood in the United States has been tested for HIV. Therefore, the risk of infection through transfusion of blood or blood products is extremely low. The U.S. blood supply is considered to be among the safest in the world.

For more information, see "How safe is the blood supply in the United States?")

Some health-care workers have become infected after being stuck with needles containing HIV-infected blood or, less frequently when infected blood comes in contact with a worker's open cut or is splashed into a worker's eyes or inside their nose. There has been only one instance of patients being infected by an HIV-infected dentist to his patients.

For more information, see "Are health care workers at risk of getting HIV on the job?" and "Are patients in a health care setting at risk of getting HIV?" If you would like more information or have personal concerns, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español.