Sometimes, when mouths and penises do stuff together, people end up ingesting semen—it's simply a part of life. Usually, it's a conscious decision. Other times, it sneaks up on you; you have nowhere to spit it out, and down the hatch it goes.
But what happens when you swallow semen, anyway—besides an ensuing struggle to figure out what it tastes like? Does it have any nutrients? And what about the STI risk of swallowing semen?
First up: What is semen made of?
It's not just sperm. As Nelson Bennett, a urologist at Northwestern Memorial, previously told Men's Health, semen is 80 per cent water. "It also contains proteins and amino acids," Bennett said. "It has fructose and glucose (both are sugars), zinc, calcium, vitamin C, and a few other nutrients."
Did someone say protein? There isn't much of it: According to Healthline, a 2013 review of studies published in the Journal of Andrology found that the average protein concentration of semen is 5,040 milligrams (mg) per 100 ml. And since the average ejaculation expels roughly 5 mL of semen, that means there are roughly 252 mg of protein in a single, er, serving.
Semen also has very few calories, Justin Lehmiller, Ph.D., a research fellow at the Kinsey Institute and author of Tell Me What You Want, explained in a 2014 blog post on swallowing semen. "Most estimates I’ve seen put the number of calories in a 'serving' of semen somewhere between 1 and 5," he wrote.
Is swallowing semen bad for your health?
"Considering it's a bodily fluid, it can be a contaminated STI risk," says Dr. Evan Goldstein, D.O., a proctologist who specializes in men's sexual health at Bespoke Surgical. "STIs such as chlamydia, gonorrhoea, and HPV—as well as HIV—are such risks." (Yes, there is still a risk of contracting HIV through oral sex, even if the risk is lower than it is for penetrative sex.)
But the STI risk isn't specifically about swallowing semen; "It doesn’t really matter whether you swallow his semen or spit it out—the risk comes from having ejaculate in your mouth," Lehmiller wrote in his 2014 post. That's why Lehmiller suggests using a condom for oral sex if you're unsure of your partner's STI status.
There's been research on whether gargling Listerine after oral sex can reduce your risk of certain STIs, but the verdict's still out on how effective it really is, according to Verywell Health. So once more for the people in the back: Using a condom is still your safest bet.
The only other potential health risk of is if you have g a semen allergy—medically known as Hypersensitivity to Human Semen (HSS). Again, this doesn't just pertain to semen swallowing, but overall semen-in-mouth exposure.
"The symptoms of HSS can vary, but at the very minimum, they usually involve redness, swelling, and itching in the genital area that begins within an hour after semen exposure," Lehmiller explained in a 2014 post on the condition. "However, some women experience more severe symptoms, and at least a few have had anaphylactic reactions, which are potentially deadly."
So what's the bottom line about swallowing semen? In his post on swallowing semen, Lehmiller concluded, "It is pretty clear that as long as the male partner is uninfected and the receptive partner is not allergic to his semen, it is unlikely that swallowing semen will have any negative effects on one’s health."