I have a question regarding STI’s with oral sex and my overall risk.  A few days ago, I received a massage from a therapist. I do not know her STI status. After about 20 mins, I flipped over and she unexpectedly put her mouth on the tip/head of my penis for approximately 3-5 seconds, after asking her to please stop. 

My question is, what is my overall risk for STI’s including HSV, HIV, etc being that it was such a quick action. I asked her to stop immediately but I’m still concerned. Mainly because I think that she may have had dentures and did not have them in at the time. If that is the case, I would be exposed to her gums, which is where my concern lies. Do I need to get on PreP? I’ve read stories that seem to be conflicting on whether is available after oral sex exposure. Thank you for your answer and all that you do within this forum. 

This was zero risk for any and all STIs, or so close to zero you can ignore it. First, it is statistically unlikely the massage therapist has an oral STI. Second, even if she did, transmission generally requires deep and probably more prolonged penetration:  saliva itself doesn't transmit infection, and STIs generally are not localized in the front part of the mouth -- only the pharynx (back of the throat). And as you suggest yourself, the brevity of the contact also argues against significant transmission risk. As for HIV and PrEP, in the 4 decades of the known worldwide HIV/AIDS epidemic, there has never been a scientifically proved case of HIV transmitted oral to penis. That doesn't mean it can't happen, but the risk is obviously in there range of once in millions. (Based on how people say they think they were infected -- which often is wrong -- CDC has calculated the risk as one chance in 20,000 if the oral partner has known, untreated HIV. That's equivalent to receiving BJs once daily for 55 years before transmission of the virus might be likely. And even the presumes a few minutes of deep penetration.)

I do not advise testing for anything; and if you have a regular partner, you can safely continue your usual sexual practices without risk of transmitting anything.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

That completes the two follow-up exchanges included with each question and so ends this thread. Thanks for the thanks; I'm glad to have helped.