The HIV virus only survives under the warmth and moist conditions of human body-(can't survive in mosquitoes for instance). Apart from that, it won't last more than a few seconds. Inside the body, it's present in significant number in tissues and bodily fluids, but not in others.

It's not such "significantly" presence- so much so as to infect someone else- through tears or saliva. Therefore, one can't catch HIV on a peck or wet kiss, or by simple sneeze. As it doesn't permeate through the skin, thus it can't be transmitted through a hug or handshake. Also, there can't be caught on a toilet seat let alone by sharing a glass, towel or toothbrush. Sharing toothbrush isn't a recommendable practice, as friction against gums may induce bleeding if prone, increasing the likelihood of transmition - due to the presence of blood and not saliva, though.

The HIV virus thrives on bodily fluids (sperm and vaginal fluid). Nevertheless, transmission takes place when blood or secretions of someone infected is exposed to someone else's body fluids. As for blood, it can occur though two manners. Though blood transfusion, when blood, or byproduct employed, hasn't been properly checked.

Moreover, when those who use injectable drugs share syringes, for a needle always has blood remnants of all participants. Sharing makeshift tube-like for snarling cocaine is highly risky as well, as decay caused of the nasal septum by the drug, exposes blood vessels promoting the virus bypass. Infection being possible through sharing septic instruments such as dental surgical, surgical or shaving gear, piercing and manicure.

As far as sexual fluids go, transmition takes place when getting in contact with the blood stream- only prevented by means of safer sex-cling film or condoms.
During sexual intercourse, rubbing tissues bursts minute blood vessels in the penis, anus and vagina, creating the right environment for infection. It occurs in penis-vagina contact, penis-anus contact or vagina-vagina.

Given that, the HIV virus can't bypass the skin, so long as there are no microscopic wounds or scratch-like, even though sperm or vaginal fluid might be exposed to the skin, there's no reason for panic. Enjoy it with no fear. In oral sex, it's also recommendable wearing condoms for fellatio or cling film for cunnilingus. As frequently tiny mouth ulcers or chapped skin unknowingly by the person, mostly like tooth decay and gingivitis lurk around.