Transmitting herpes via oral sex?

[mr_hopp]

Hi H Oppers!

A question I received via email that I'll share here just in case you've pondered the same thing:

"What confuses me about herpes is the following: If a man performs oral sex on a woman who has genital herpes, can he contract oral herpes? If a woman has oral herpes and performs oral sex on a man, could she transmit genital herpes to him?"

[mr_hopp]

Assuming there is no active outbreak, of course, then we're talking about the risks of transmission from the herpes-positive partner's genitals to the herpes-negative partners's mouth via asymptomatic viral shedding. Whether it's a woman's mouth or a man's mouth who is doing the oral sexing, the rate of transmission to that mouth will be the same. The difference between sexes is in genital transmission rates, which lies in the fact that penises have less mucous membranes than vaginas, so women are ~2x as likely to get genital herpes than men — 15.9% of women have HSV-2 vs. 8.2% of men. [CDC]

Back to the oral transmission rates ... specifically answering the first question (genital-to-oral transmission), there are different scenarios (see the free handouts for the % breakdown):

• If the partner has genital HSV-1: Genital HSV-1 only sheds 3-5% per year (vs. genital HSV-2 shedding 15-30% per year), so yes, genital HSV-1 can be transmitted to a partner's mouth, but interestingly you have about 3x more of a chance of transmitting oral HSV-1 through kissing than through oral sex. This is because oral HSV-1 sheds about 3x more (9-18% per year) than genital HSV-1 (again, 3-5%). So in other words, 2/3 of the world has HSV-1, so whenever people kiss, they are taking 3x more of a risk of getting oral HSV-1 (if they're the minority of 1/3 of the world who doesn't have HSV-1 yet) than if they were to go down on a partner who happens to have genital HSV-1. Food for thought.
• If the partner has genital HSV-2: Genital HSV-2 sheds more (9-18% per year) than genital HSV-1 (3-5%), however HSV-2 much prefers to stay below the belt than above. In fact, only 1-2% of all HSV-2 cases are oral. So it’s much more difficult to transmit herpes orally, even if the shedding rates are higher. 

Then for the other part of your question (oral-to-genital transmission), yes, this is common. In fact, of all new genital herpes cases, more than half of them are via oral sex! This happens mostly out of ignorance because people don't realize that those super common "cold sores" that most people get are actually oral HSV-1 and can be transmitted genitally and (*magically*) become genital herpes of the HSV-1 variety. Again, there is twice the risk of a herpes transmission to a vagina via oral sex than a penis because more mucous membrane. 

I hope this helps!