Dr. Susie Gronski


Does Semen Upset Vaginal Flora?

Sorry to bum you out, folks, but having penis-in-vagina (PIV) sex can result in some nasty infections that aren’t technically STIs. That’s because the pH levels of semen are higher than the pH levels of vaginas, which can mess with the growth of healthy bacteria or “vaginal flora.”

Confused? I’ll explain.

Vaginas are acidic and semen is alkaline. Chances are, you haven’t heard those two words since high school chemistry class, so let’s back up a little. Acidity and alkalinity are measured by pH, with zero being the most acidic and 14 being the most alkaline. Anything under seven is on the acidic side of things, while anything over seven is on the alkaline side. Healthy vaginas have a pH between 3.8 and 4.5, which makes them slightly acidic. Semen, on the other hand, is between 7.1 and 8 — making it slightly alkaline.

Still with me? Good.

In order to stay healthy, a vagina needs to maintain that delicate 3.8 to 4.5 pH balance. That’s the sweet spot for growing Lactobacilli — a healthy bacteria that vaginas need — and also for killing off harmful bacteria that might try to sneak in and hang out. But, if you’ll recall from two paragraphs above, semen is over those numbers, clocking in at a minimum 7.1. As a result, semen can potentially disrupt that delicate balance that’s ideal for vaginal flora and make the vagina more alkaline. Key word here is potentially. There are a lot of other factors that can disrupt your vaginal flora like diet, stress, hormones and gut health. So don't go blaming your partner just yet.


And guess what happens then?

Those bacteria — like yeast and the bacteria that cause bacterial vaginosis (BV) — that weren’t able to grow in an acidic environment sneak in and start growing. And by “growing” I mean “causing annoying, itchy, painful, smelly infections.”


But, if you’re a person with a vagina having sex with a person with a penis, there are steps you can take to avoid the above messy, itchy, smelly situation. The first one is condoms, because (obviously) then no semen gets introduced to the vaginal canal. The second one is making sure to always pee after sex, in order flush some of that semen out. Another good move is to make a shift in your diet, as both sugar and carbs can upset gut and vaginal flora, especially if you’re prone to yeast infections. Eliminating or reducing those foods in your diet can help keep a healthy balance.

You can also wash with warm water, but heads up: The pH of water is 7, so it can potentially contribute to the problem. One thing you don’t want to do is wash with soap or douche, as both of those moves are prime culprits for upsetting vaginal pH.

And, as many of you probably know from personal experience, having vaginal intercourse with no barrier and then forgetting to pee afterward isn’t going to cause an infection every time. Those harmful bacteria have to be hanging out and ready to jump in as soon as that pH balance goes off and if they’re not, you’re good.