The risk of acquiring HIV during oral sex (sucking the penis of an HIV-positive person) is pretty low, but it isn't zero. Taking your partner's ejaculate (cum or pre-cum) in your mouth appears to make transmission more likely. Almost all of the individuals who say that oral sex must have been the way they acquired HIV and whose cases have been medically evaluated mention that they took ejaculate in the mouth.
It isn't actually the swallowing that matters, it's probably having the ejaculate in your mouth (especially if there are any cuts or ulcers there). In the stomach, digestive enzymes and acidity may inactivate HIV.
But the risk of acquiring HIV during vaginal or anal sex is far, far higher than during oral sex. It's also worth remembering that when a person with HIV receives antiretroviral treatment, the amount of HIV in his body fluids falls dramatically. Put simply there will be very little HIV in his semen, so transmission is highly unlikely. This applies to all forms of sex, including oral sex.
More on Oral Sex at TheBody.com
To find out more about the risk from oral sex, we recommend the following articles:
In addition, our Q&A experts sometimes address questions about oral sex in our "Ask the Experts" forums. Here are some of those questions and our experts' responses:
- swallowing, increased risk of transmission?
You note that the transmission risk of receptive oral sex is 1 per 10000 exposures. Does that risk increase if ejaculate is swallowed?
- Can I get HIV from pre-cum?
About 2 months back I had unprotected oral sex with a man, but I didn't swallow when he ejaculated. Naturally however, there was pre-cum and I'm very scared that I might have HIV.