Every Friday, I answer people’s questions about sex, love, and relationships. This week’s question comes from a reader who wanted to know the following:
“Is the ingestion of a man's ejaculate harmful?”
Good question! There are a lot of misconceptions out there about semen and its effects on health, so let’s take a few moments to separate fact from fiction.
First, if you perform oral sex on a man who has an STI (e.g., chlamydia, gonorrhea, HIV), you run the risk of contracting his infection. And it doesn’t really matter whether you swallow his semen or spit it out—the risk comes from having ejaculate in your mouth. So, if you know your partner has an infection or you aren’t sure of his status, it would be advisable to use a condom to prevent contact with his semen, thereby lowering your own infection risk.
Assuming he is uninfected, there are very few risks associated with having his ejaculate in your mouth or swallowing it. For starters, it’s not going to make you fat. I’ve had some people ask whether semen is loaded with calories, and the answer is no. In fact, most estimates I’ve seen put the number of calories in a “serving” of semen somewhere between 1 and 5.
Also, women don’t need to worry about pregnancy from swallowing semen because sperm deposited in your digestive tract won’t be able to make it into your reproductive tract…unless you get stabbed in the stomach after performing oral sex (which is pretty unlikely). I don’t want to turn this into a sideshow, but I did read one case a few years ago of an African girl who was performing oral sex on her boyfriend when her ex walked in on them . Apparently a knife fight ensued and she was stabbed in the stomach. Soon after, she discovered that she was pregnant. After visiting a doctor, the mode of conception was attributed to her stabbing. Of course, you're probably wondering, "But isn't this pregnancy more likely the result of vaginal intercourse?" It turns out that wouldn't be possible in this case because this girl did not have a vagina. She had a genetic condition (Mullerian agenesis) that prevented its development, leaving just a small dimple in the spot where the vagina normally appears. In light of this, the post-oral sex stomach wound seemed to provide the most plausible means of sperm reaching her reproductive tract. I know this story seems hard to believe, and I have my doubts about a pregnancy happening this way, but it was published as a case report in a medical journal.
Aside from potential STI transmission and random stomach stabbings, the only other risk I’m aware of with regard to swallowing ejaculate would be if the receptive partner has a semen allergy. For more on semen allergies, check out this article. Related to this, I have also heard of some cases of “semen ingested induced diarrhea,” in which swallowing semen leads to some serious gastrointestinal distress (perhaps as a result of a fructose intolerance, given that fructose is one of the primary components of semen); however, this is thought to be quite rare.
Are there any benefits of swallowing semen? Believe it or not, I read one study a few years back that found a correlation between swallowing semen and risk of preeclampsia (in case you’re unfamiliar, preeclampsia is a condition that tends to occur late in a pregnancy in which a women develops very high blood pressure—if left untreated, this is potentially fatal to both the mother and the fetus). What the researchers found was that women who swallowed more semen through oral sex tended to have a lower risk of developing preeclampsia. Why? The basic idea is that a fetus is exposing its mother to foreign antigens because half of its genetic material is provided by the father. To the extent that a woman is exposed to more of these antigens prior to pregnancy, she may develop a tolerance to them, thereby reducing her risk of having an immune reaction in response to the fetus.
That said, research on the potential benefits of swallowing semen isn’t conclusive enough to say that everyone should be doing it; however, 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.
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 Douwe, A.V. (1988). Oral conception. Impregnation via the proximal gastrointestinal tract in a patient with an aplastic distal vagina. Case report. British Journal of Obstetrics and Gynaecology, 95, 933-934.
 Koelman, C. A., Coumans, A. B., Nijman, H. W., et al. (2000). Correlation between oral sex and low incidence of preeclampsia: A role for soluble HLA in seminal fluid? Journal of Reproductive Immunology, 46, 155–66.
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