Oral sex is not a major route of transmission for HIV and hepatitis B. The risk of HIV is practically zero, but there are some circumstances in which this risk rises slightly, albeit still being relatively low risk. Please see the diagram on the right.
The risk of hepatitis B is about 1% in all oral contacts (mouth to penis and cunilingus)
How can this risk be calculated unless people tell the truth?
It is extremely difficult to calculate the risk of HIV in oral sex because you have to identify people with the disease who have only ever practised unprotected oral sex, and often don’t want to admit the truth about other kinds of sex.
This situation is well illustrated if you read one study (that reports that in the UK only 13 cases of HIV were transmitted in oral sex from the 1980s up until 1998) with other studies published more than 15 years ago where a higher risk was reported, suggesting that oral sex is probably not a major route of transmission.
Beware of reading studies from the pre-medication era, because they conflict with the general consensus:
These studies also have tried to quantify risk. Some of them report a rate of between 3 and 16% of all positive cases being due to oral sex. But this is NOT our experience in Open House nor does it coincide with estimates made by health authorities. Also, these studies were performed in the pre-medication era, and this treatment dramatically reduces the infectivity of people with HIV.
- Wound or abrasion on the genitals
- Wound or abrasion in the mouth
- Brushing teeth immediately before sex
- Ejaculation (risk for the person who receives)
- Co-transmission of gonorrhoea or chlamydia
- The use of drugs during sex
- Having syphilis
The risk of HIV in oral sex is zero in normal circumstances. If one of the following factors is present, then the absolute risk is low but not zero, and is around 0.01 to 0.05%.
We have done about 8000 HIV tests in people whose only contact was oral sex. Around 250 of these cases the sex was someone known to have HIV.
To date, we have only seen two possible cases in oral sex and they were due to co-transmission of syphilis occurring at the same time.