Everything You Ever Wanted To Know About Semen

This story was originally published on December 23, 2014.

By Kendall McKenzie

Most people don’t spend a whole lot of time thinking about semen, but the spunky gunk is a pretty amazing concoction. Whether it ends up in a tissue, condom, or bodily orifice, jizz all comes from the same humble beginnings and goes on the same wild ride.

Sperm Vs. Semen
Even though people often use them interchangeably, sperm and semen aren’t the same thing. Semen (a.k.a. cum) is the gooey fluid that spurts out of the penis during ejaculation, and sperm are the microscopic, tadpole-looking cells inside semen that cause pregnancy. You can think of sperm as fish, and semen as the river.

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The Sperm Journey
Sperm are produced at a rather impressive rate. Testicles contain nearly 1,200 feet of spaghetti-like tubes that produce around 1,000 sperm cells per second, round the clock. It’s a continuous, but not instant, process — the full development of one sperm cell from start to finish takes about 90 days. After growing in the testicles for a couple months, sperm head to the epididymis, their storage facility in the scrotum, where they mature until they’re ready to be sent on their grand egg-seeking journey. If sperm aren’t invited to an ejaculation party within a few weeks, they’re reabsorbed back into the body and replaced by fresher batches.

When sexy times come a knockin’, the mature sperm chilling in the epididymis get pumped through two tubes, called the vas deferens, up to the semen factories: the seminal vesicles and the prostate. Each of these glands lives next to the bladder and adds its own distinct ingredients to semen, to help nurture and protect sperm. Ejaculation mixes sperm with various parts of semen and splooges the whole magic cocktail out of the body at around 10 miles per hour.

Magical, Magical Semen
Even though there are roughly 200-500 million sperm cells in every ejaculation, sperm only make up about 1% of semen — the rest is all about protecting and nourishing that precious cargo. The majority (50-70%) of cum comes from the seminal vesicles, which produce a thick liquid rich in fructose sugars that provide energy for sperm. The prostate contributes to up to 30% of semen, releasing a thin, milky, alkaline fluid that helps the little swimmers move and counteracts sperm-killing acidity in the vagina.

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The vagina’s acidic pH is designed to attack germs and other intruders, but our bodies work together to help sperm survive. In fact, the alkaline nature of semen actually raises the vagina’s pH temporarily, creating a safer environment for sperm so they can they reach the hospitable cervix. The cervix is generally more sperm-friendly than the vagina (especially around ovulation), so both cervical fluids and semen act as protective buffers.

Both the seminal vesicles and the prostate secrete chemicals responsible for yet another sperm protection mechanism: coagulation. If you’ve ever noticed how fresh semen starts out clumpy and then slowly liquefies, you’ve seen this effect in action (though consistency varies from person to person). Proteins from the seminal vesicles cause semen to clot right after ejaculation, which is believed to serve a pretty important double purpose: holding sperm up near the opening of the cervix and protecting them from the acidic vagina. Over the next 20-30 minutes, an enzyme secreted by the prostate gradually thins out the gel-like glob. This liquefaction releases sperm from the semen, allowing them to continue on through the cervix, into the uterus.

Fertilization (when sperm penetrate an egg) doesn’t typically happen right away: sperm can survive in the cervix, uterus, and fallopian tubes for several days after sex. Around ovulation time, cervical mucus has optimal pH levels and sugars to protect and nourish sperm, and its watery consistency makes for smooth swimming through the cervical opening. But, cervical mucus can also be a real sperm buzzkill: many types of hormonal birth control (like the implant) and IUD prevent pregnancy by making it too thick for sperm to get through. AREN'T BODIES AMAZING?

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Illustrated by Sydney Hass.

What’s The Deal With Pre-Cum?
Just like semen, pre-ejaculate plays an important role in sperm survival. The slippery stuff that drips out of the penis when things start getting zesty is made in the cowper’s glands (also called bulbourethral glands). Pre-cum lubricates the urethra and helps neutralize acidity from urine residue, prepping sperm’s pathway for a safe, smooth ride. Everyone with a penis makes pre-cum during arousal, even if it’s not always noticeable.

One of the most common questions about pre-cum is whether or not it contains sperm cells (and can therefore cause pregnancy). Pre-cum itself doesn’t contain sperm, but it may push out sperm that are hanging out in the urethra. So it’s possible, though unlikely, to get pregnant from pre-cum — that’s one reason why the pull-out method doesn’t always work.

How Do Vasectomies Work?
Vasectomies are one of the few birth control options for the penis-carrying set. (They’re also super effective, and usually permanent.) But, a big misconception about vasectomies is that they turn the faucet off altogether, resulting in totally dry, ejaculation-less orgasms.

In reality, vasectomies don’t stop ejaculation, they just stop it from causing pregnancy. A vasectomy snips or blocks the vas deferens (hence the name), keeping sperm safely in the testicles and away from semen. Both sperm and semen are still produced, but they can’t party together anymore — semen goes on its merry way out of the penis, and sperm get reabsorbed back into the body. And, because sperm only make up a miniscule portion of ejaculate, the difference in volume and consistency after a vasectomy usually isn’t noticeable.

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What You Put In Your Body May Impact What Comes Out Of It
One of the more lively spunk debates is whether or not food and drink alter its taste, but there’s not enough research to determine for sure which side is correct. It’s generally believed that sugary stuff like fruit can make it taste sweeter; things like meat, coffee, and alcohol may make it a little more bitter. Everyone’s body is different, and semen taste varies from person to person.

Some chemicals in drugs like alcohol, cigarettes, weed, cocaine, and heroin can affect sperm count or the quality of semen, making it difficult to cause pregnancy. However, these are NOT reliable forms of birth control (mother nature can be so picky!). So it’s a good idea to stay away from that stuff if you’re trying to get pregnant, and you should be on a real method of birth control (like the pill or IUD) if you’re serious about preventing pregnancy. While drugs may alter sperm health, they don’t pose any risks for partners exposed to that semen. For example, marijuana in your boyfriend’s system won’t get transferred to your body through his cum.

What semen can spread, however, is STDs, and you can’t tell if someone has one by the look or taste of their spunk. The only way to know for sure is to get tested.