A leading blog on the science of sex, love, and relationships, written by social psychologist Dr. Justin Lehmiller. Good question! First, if you perform oral sex on a man who has an STI e. Assuming he is uninfected, there are very few risks associated with having his ejaculate in your mouth or swallowing it.

We do not give warnings.
It's mostly made up of harmless nutrients—so how bad could it be?
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Can Your Stuff Be Making Her Sick?
The Situation: Your friend loves sex—but she's not exactly tied down to one guy, and even when she is, one fact remains constant: She loves giving oral, and she always swallows. No shame in that, you think—to each her own. But what about all that man juice? The Reality: Semen is made up of the same harmless nutrients, minerals, and sugars that you probably eat every day—stuff like vitamin C, potassium, calcium, and fructose. Sperm cells actually account for a very small portion of semen. Still, it can't replace your peanut butter protein shake: A man only produces about a teaspoon of semen per orgasm, and that's not nearly enough to provide any health benefits—even if you're getting it daily. But it also doesn't contain any seriously foreign ingredients, and your body digests it like any other sustenance you eat, says Debby Herbenick, an associate professor at Indiana University School of Public Health. The real danger lies in the risk of infection before you swallow.
Sperm — about 1 to 5 percent of the semen — are the tadpole-like reproductive cells that contain half of the genetic information to create human offspring. The seminal plasma fluid, which is about 80 percent water , makes up the rest. For the most part, yes, the components that make up semen are safe to ingest. This is also known as human seminal plasma hypersensitivity HSP. Though rare, this sensitivity is something to be aware of in case you find yourself experiencing an allergic reaction.