HIV is quite a difficult virus to transmit. Infection can only happen when infected bodily fluids come into contact with broken skin or mucous membrane such as those in the rectum, penis or vagina. The bodily fluid needs to contain enough virus to be infectious. Those fluids are blood including menstrual blood , semen, vaginal fluid, rectal fluids, and breast milk.
There is not enough HIV in saliva, urine or tears for it to be infectious. HIV is most commonly transmitted via unprotected sexual intercourse. Sharing needles when using drugs is also very risky. You can protect yourself from HIV by practicing safer sex and safer use. The risk of HIV transmission is higher if there is a large amount of virus in the blood and bodily fluids.
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This is the case two to four weeks after an initial HIV infection, when the virus is replicating itself very rapidly.
The risk is much smaller when there is only a small amount of virus in the blood, for example when HIV therapy is preventing the virus from replicating. There is very little virus present in spit, tears or urine. It is therefore not possible for the virus to be transmitted by these bodily fluids. Outside the body, the virus is only able to survive for a very short time and can be easily killed by normal hygiene procedures.
HIV is most commonly transmitted via unprotected anal and vaginal sex. Semen, vaginal fluid and menstrual blood may contain much HIV. The mucous membranes of the rectum and vagina are very sensitive and can easily absorb the virus, as can the inner surface of the foreskin and the urethra. However, this risk is much lower than with anal or vaginal sex because the mucous membrane of the mouth is much more resistant to HIV than other mucosas. When ingesting vaginal fluid which does not contain blood, the amount of virus is too small for an infection.
