Factsheet Oral sex

Many people find oral sex an intensely pleasurable experience. People use different terms to refer to oral sex (including formal terms like fellatio and cunnilingus and slang terms like blow jobs and giving head). Usually oral sex means one person kissing, licking or sucking another person's genitals.

Doctors and researchers can't be sure how many people have acquired HIV through oral sex. In late 2008, researchers looked at all the available evidence and calculated that the risk of acquiring HIV from oral sex was very low, but that it wasn't zero. It is clear that oral sex involves much less risk than anal or vaginal sex.

The likelihood that HIV is transmitted from a person living with HIV to an HIV-negative person depends on the type of contact involved and the viral load of the person living with HIV.

HIV is most easily passed on during anal sex, vaginal sex, sharing injecting equipment, and from mother to baby. It is much less likely that HIV will be passed on during oral sex, but it is possible in some circumstances. It depends on the viral load of the person living with HIV and the dental health of the person performing oral sex.

It’s also worth remembering that other sexually transmitted infections, such as syphilis, herpes and gonorrhoea, can be quite easily passed on through oral sex. It's a good idea to have regular sexual health check-ups.

The risk of HIV being passed on during oral sex centres on fluid containing HIV (semen, vaginal fluid or blood) finding a way into the bloodstream of an HIV-negative person (via the mouth or throat, which is more likely if there is inflammation, or cuts or sores present). HIV is not passed on through exposure to saliva alone, so a person with HIV performing oral sex on someone who is HIV negative is not considered to be a transmission risk.

The type of oral sex makes a difference to the level of risk.

• HIV transmission through 'receptive fellatio', which means an HIV-negative person performing oral sex on (giving a blow job to) a man with HIV is possible and it is likely that HIV transmission happens in this way sometimes.
• There have been very few reports of possible HIV transmission through cunnilingus (oral sex performed on a woman). It is biologically possible that HIV could be passed on through an HIV-negative person performing oral sex on a woman living with HIV, but this is considered to be low risk.
• HIV transmission through 'insertive fellatio', which means an HIV-negative man receiving oral sex from a person living with HIV, is very low risk and may be impossible.
• There have been no documented cases of someone acquiring HIV through receiving cunnilingus from someone living with HIV.

The other factor that makes a big difference to the potential risk of HIV transmission from oral sex is the viral load of the person living with HIV. Viral load is the term used to describe the amount of HIV in a sample of body fluid. People living with HIV have the viral load in their blood measured regularly, as part of routine health monitoring.

When a person living with HIV is taking effective HIV treatment, their viral load should decline until it is so low that it cannot be detected by the tests. This is referred to as an ‘undetectable viral load’. This does not mean the person is cured of HIV, and if they stopped taking treatment their viral load would go back up.

There is good evidence that when someone is taking treatment and has an undetectable viral load, they cannot pass HIV on through sexual activity – including oral sex.

If you are living with HIV, there is a higher risk of passing on HIV through someone performing oral sex on you, if you are not taking treatment and if you also have an untreated sexually transmitted infection. If you don't have HIV and you are performing oral sex on someone who does have HIV, you are at more risk of acquiring HIV if you have cuts, sores or abrasions in your mouth or on your gums. There is also more risk if you have an infection in your throat or mouth which is causing inflammation.

"It is clear that oral sex involves much less risk than anal or vaginal sex."

For men, having a high viral load in the blood may also mean that viral load is high in the semen. Factors like untreated sexually transmitted infections can cause viral load in semen to increase.

For women, the levels of HIV in vaginal fluid vary. They are likely to be highest around the time of menstruation (having your period), when HIV-bearing cells shed from the cervix are most likely to be found in vaginal fluid, along with blood. Oral sex will therefore be more risky around the time of menstruation.

There are several ways to reduce the risk of HIV transmission from oral sex. Naturally, some will be more acceptable than others to different individuals, so you must make your own decisions about the level of risk you find acceptable. If you would like to discuss these issues, ask to see a health adviser, or other health professional, at your HIV treatment centre or sexual health clinic. Many of the strategies below will also provide protection against other sexually transmitted infections:

• You may decide that the risks of oral sex are low enough for you to continue your regular behaviour.
• You may prefer not to have oral sex because you do not wish to take even a low risk of HIV transmission.
• You may decide to reduce the number of partners with whom you have oral sex.
• You may decide to have oral sex with barriers such as condoms for men or dental dams (latex squares) for women.
• If you don't have HIV, you may decide only to have insertive oral sex (someone giving you oral sex) as this is safer than receptive oral sex (giving someone else oral sex).
• You may decide not to ejaculate into your partner’s mouth or not to have someone ejaculate into your mouth.
• You may decide to avoid oral sex during menstrual periods.
• Look after your mouth. The likelihood of becoming infected through giving oral sex increases if someone has bleeding gums, ulcers, cuts or sores in the mouth. Don’t brush your teeth or floss just before oral sex.
• Have regular sexual health screening. This will identify if you have any sexually transmitted infections, which may increase the likelihood of you passing HIV on to an HIV-negative partner, and reduce the likelihood of you acquiring HIV if you are HIV-negative.

If you are living with HIV, taking HIV treatment as prescribed, so that you maintain an undetectable viral load is the most effective way of preventing HIV being passed on.

If you are HIV negative and are concerned that you may be vulnerable to acquiring HIV, you may want to consider taking pre-exposure prophylaxis (PrEP).