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20 Things You May Not Have Known About Semen

"Pre-cum" does not actually contain any sperm. That doesn't mean you shouldn't be careful with it, though.

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Charlotte Gomez for BuzzFeed

BuzzFeed Science had the opportunity to chat about semen with Dr. Abraham Morgentaler, a clinical professor of urology at Harvard Medical School, the author of Why Men Fake It: The Totally Unexpected Truth About Men and Sex, and the founder of Men's Health Boston, his own private medical practice. It turns out semen is pretty freaking baller, and we have the facts to prove it.

1. Sperm and semen are not the same thing.

Spermatazoa, or sperm, is the name given to the reproductive cell that looks like a tadpole. Seminal fluid is the stuff that the tadpole swims in. Together they form semen — an armored tank carrying a fertilization superhero. Or, as Morgentaler calls them, "heat-seeking missiles."

2. Seminal fluid is the sperm's sacred protector.

Seminal fluid helps sperm "do their biologic mission" as Morgentaler calls it, by helping the sperm get into the female body. Seminal fluid is alkaline, so it reduces the acidity sperm experiences in the female reproductive system. And, perhaps most important, seminal fluid gives the sperm the energy (in the form of fructose) they need for their arduous swim.

3. Semen is formed in three different parts of the body, not just the testes.

According to Morgentaler, semen comes from three main structures in the male reproductive anatomy. The first is the prostate, which forms a milky substance full of enzymes, proteins, and minerals. The second are the seminal vesicles, which produce the fructose as well as two-thirds of the fluid. The third are the testicles, which produce the sperm and some other fluid as well.

4. Sperm are the only human cells produced in one individual, but designed for survival in another.

"Sperm are amazing," Morgentaler says, because of this fact. Think about it! Our bodies are designed to attack anything that is not from our own body. Sperm didn't get that memo, though. Not unlike the white-haired traveler Anthony Bourdain, sperm, too, venture on to parts unknown.

5. Dudes produce a shit ton of sperm.

According to Morgentaler, a human male produces around 150 million sperm a day. That means you are producing a few thousand sperm every couple of seconds.

6. Most of a man's sperm are pretty useless.

According to Morgentaler, "guys are into quantity and not so much quality." Only a bit more than half the semen in an average ejaculation can swim, he says, and up to 70–90% are not ideally shaped for swimming. We are talking two heads, two tails, big heads, small heads, big tails, small tails, no tails… it's a hot (literally) mess (sometimes literally).

7. Semen is protected from your body's immune system so that your own body doesn't attack it as a foreign substance.

Sperm does not begin to form in a male's body until he hits puberty. By that time your body's immune system has already decided which kinds of cells are part of the human body and which are not. That means, according to Morgentaler, that left to it's own devices, your body would attack sperm as an invader. That's why the testiciles are shielded (in many complex ways) from the rest of the body. The testes are what is referred to as an "immunologically privileged site."

8. When semen is first ejaculated, it is a gel. It transforms into a liquid afterward.

This change is caused by an enzyme called PSA. Though Morgentaler cautions it is speculative, some think that the reason for this is that a gel is less likely to be subject to gravity and can stay in the vaginal tract more successfully. Because of this, doctors generally have to wait about 20 minutes before analyzing semen under the microscope so that it is in a fully liquid state.

9. Semen is mostly water.

Charlotte Gomez for BuzzFeed

And it is only about 1% sperm, says Morgentaler. It's also got a bunch of other good stuff in there like calcium and fructose and tons of other enzymes and minerals.

10. On average, men ejaculate about a teaspoon's worth of semen.

Morgentaler says the average ejaculate is about 1.5 ml to 5.0 ml.

11. Semen also contains protein. The same kind found in egg whites!

The protein in question is called albumin, and Morgentaler says it's found in most of the fluids in the human body.

12. It's fairly low-calorie! Each ejaculation contains about 10 calories per teaspoon.

Not shocking, since it is mostly water.

13. Still, semen is not a great source of nourishment.

Pro tip: Don't use the nutritional content of semen as an argument to convince someone (or be convinced yourself) to do something they or you are not comfortable with. According to Morgentaler, semen has the nutritional content of "a couple of insects."

14. You can't catch the common cold from semen alone, but you can get some other sexually transmitted diseases.

Semen on its own cannot carry something like the common cold. That doesn't mean other fluids exchanged during sexual activity can't. Semen CAN, however, transmit many other STIs.

15. Pre-ejaculate, or "pre-cum," does not actually contain any sperm.

Many of us were taught in sex ed that the semen that comes out of a man's penis before he orgasms can cause pregnancy. Most of Morgentaler's med students hold this view before his class as well. But it is not, scientifically speaking, true. The pre-ejaculate comes from a different gland entirely, the Cowper's gland, and it is thought to provide a lubricant for the semen that comes from ejaculation. That being said, if you had recently ejaculated, your pre-ejaculate could pick up some leftover sperm on its way out, so it's always good to be cautious.

16. Things that you eat and drink can affect your semen.

First and foremost, how hydrated one is can affect the volume and viscosity of his ejaculation. There is also plenty of anecdotal evidence to suggest that diet can affect semen's taste, though Morgentaler notes that few studies have actually been performed that address this topic, and that "taste is in the tastebuds of the beholder."

17. There hasn't been much science to support claims that supplements can increase the volume of a man's ejaculation.

Past hydration and holding off from ejaculating for a bit, there isn't much one can do to change the volume of their ejaculation. According to Morgentaler, there isn't much science behind other methods or supplements.

18. When you get a vasectomy, you still ejaculate almost the same amount of fluid as before the operation.

A vasectomy is an operation that disconnects the vas deferens, the passageway for the sperm to meet up with the rest of the semen team, from the rest of the reproductive system. Post-vasectomy ejaculations may have around 5–10% less fluid (the amount that the testes contribute to the semen), but according to Morgentaler, it is not generally all that noticeable.

19. There is no real way to test your sperm's fertility without the help of a doctor.

Sure, if someone gets pregnant, then it's safe to assume the sperm that did the deed were healthy and fertile. But a dude can't just crank one out and take a look at it himself. Doctors can perform a semen test, though, which looks at things like how well sperm swim and how much sperm is in a man's semen.

20. Bigger loads do not necessarily mean more potent semen.

In reality, there is no correlation between fertility and volume of ejaculate, Morgentaler says. In fact, there are rare cases in which it could be considered a problem. Morgentaler thinks this (relatively recent) desire for larger volume ejaculations is primarily the result of the prevalence of pornography.

Science Writer, Fossil Beastmaster

Contact Alex Kasprak at alex.kasprak@buzzfeed.com.

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