Five surprising facts about semen from a men's health expert

Semen was used to make invisible ink, in news you could never make up.

Semen was used to make invisible ink, in news you could never make up

(Credit: iStock/Getty Images)

This article was originally published April 24, 2017.

If Something About Mary taught us anything, it's to keep semen away from your hair.

But aside from its industrial-strength hair gel properties, and its role in pregnancy, what else is there to know about seminal fluid?

To answer every question you've ever had about semen, and some you wouldn't even think to ask, we asked Dr. Abraham Morgentaler, author of The Truth About Men and Sex and founder and director of Men's Health Boston, and did our own deep-dive into the complex – and sometimes sticky – world of semen.

A spoonful of semen

The average male produces between 1.5 and 5 millilitres, or 1/4 and 1 teaspoon, of semen per ejaculation, said Morgentaler. The amount varies from person to person – Morgentaler calls people who produce higher than average quantities of semen "super shooters." The amount also varies depending on how intense the orgasm is and how long it's been since the man last ejaculated – for instance, if a man had sex twice in one day, the second ejaculation might be a smaller, he said. It's not clear why some men produce more semen regularly, but the reasons why someone produces less could include having low levels of testosterone, taking certain medications, or dealing with the side effects of diabetes, Morgentaler said.

A source of protein

Semen is full of protein and naturally-occurring fructose. "The list of ingredients in semen is remarkably long and fascinating," said Morgentaler. "People have talked about whether semen could be a nourishing meal." He noted that he personally suspects the nutritional value of semen is probably a little scant and he wouldn't hazard a guess at a calorie count. Morgentaler did say this: "Nobody's going to gain weight by having a lot of oral sex."

Taste tests are... complicated

Unfortunately, there aren't many formal studies focusing on changing the taste of sperm. "I think (studies) would have trouble passing an ethics board (review)," said Morgentaler. "Taste is very subjective and you have to think: who is going to be the taster?" However, anecdotes and informal surveys suggest pineapple can be a factor in sweetening the taste of sperm, and some people believe vegetarians have "more palatable" semen than meat eaters, he said. If there is a particularly foul odour or taste, it could be due to a prostate infection, he said.

Sperm play a minor role

When it comes to pregnancy, these little swimmers are the MVPs. But when it comes to contributing to the overall volume of semen, they play a very minor role. In fact, sperm, which come from the testicles, make up just a tiny percentage of ejaculate, said Morgentaler. Seminal fluid, the other part of semen which comes from the seminal vesicles and the prostate, makes up almost all the final product, he said. And for men who've had vasectomies and some who are infertile? Sperm don't even come into play.

A multi-purpose product

In what might be every teenage boy's PG-rated fantasy come to life, it's been revealed the British secret service used semen to make invisible ink during the First World War. A diary from a senior member of MI6 tells us that the British secret intelligence service used semen because the bodily fluid apparently did not react to iodine vapour, the substance that gave away other invisible inks.   

For those skincare fanatics out there, you could even try a sperm facial. Indeed, there are plenty of online resources praising the skincare benefits of sperm, but dermatologists are mostly unconvinced.

Our advice? Unless you want super-strength hair gel, keep semen in the bedroom.

Katrina Clarke is a Vancouver- and Toronto-based journalist who writes about relationships, health, technology and social trends. You can find her on Twitter at @KatrinaAClarke.