Unprotected sex (vaginal or anal sex without a condom) is how the great majority of people become infected with HIV and other sexually transmitted infections during sex.
During unprotected sex, HIV moves from a body fluid of an infected person (blood, semen, vaginal fluids, pre-cum or anal mucus) into the body and bloodstream of their sexual partner via the delicate and absorbant mucous skin of the penis, vagina, lining of the rectum and sometimes the mouth and throat. An infection doesn’t happen every time unprotected sex takes place, but it could happen any time unprotected sex takes place.
A person can have unprotected sex with an infected person quite a few times and not get infected. But no-one should think they are immune to HIV or that they can carry on taking risks without becoming infected. The more people someone has unprotected sex with, the more chance one of them might have HIV and the greater chance the virus will be passed on.
Someone is much more likely to pass on HIV during the first few months after getting infected when he or she has very high levels of the virus in their body fluids. But during this period this person is unlikely to realise they have HIV.
The male and female condom are good at stopping HIV, especially if used properly - eg, with water-based lubricant (oil-based lube weakens condoms). If a man with HIV ejaculates inside his partner, this raises the risk of infection. Pulling out before ejaculation lowers the risk but this can be hard for men to control so shouldn’t be relied on. Also, HIV is found in pre-cum - so even if a man manages to pull out before this happens, he could infect a partner when his pre-cum gets inside his partner.
Millions of men and women around the world have got HIV through vaginal sex. Anal sex without a condom (sometimes called ‘barebacking’) has an even greater HIV risk. This is because the lining of the rectum is not as tough as that of the vagina, so it is more likely to bleed during sex. This gives HIV in infected semen an easier way into a partner’s body. Read our page on oral sex for more details.
Someone who knows they have HIV may be prosecuted and go to prison if:
- they don’t tell a sexual partner they are HIV positive
- they then have unprotected sex with that partner
- the partner gets HIV and makes a complaint to the police.
Our pages on unprotected sex and the law and viral load and infectiousness have further details.