Photo: H. Armstrong Roberts/ClassicStock

It started with a woman giving birth. As the doctor told her to push-push-push! She screamed in pain and yelled a blast of obscenities.

Her husband watched, fascinated. This woman could really cuss.

“Is this normal?” he asked the midwife, half-joking.

“Don’t be embarrassed. It’s a perfectly normal part of giving birth,” the midwife told him.

Hmmmm. This got him thinking. He happened to be a scientist, Dr. Richard Stephens, and as he told me years later, “The delivery of the baby was the starting point. In this perfectly rapturous, beautiful moment of giving birth, she’s cursing like a sailor.”

Why would his wife start dropping F-bombs? And if it’s a “perfectly normal” part of going into labor, why does everyone do it? What’s the root cause? Logically, Stephens reasoned, there must be a biological purpose for profanity. “Swearing is obviously useful; if it wasn’t useful, people wouldn’t do it,” he tells me. “We only do things that give us rewards or benefits; that’s just the way the world is.”

So he dedicated his work to proving that swearing can, in fact, give us measurable benefits. In a delightfully oddball experiment, he had a group of student volunteers dunk their hands into a tub of freezing water. He measured how long they could keep their hands in the ice water. (Stephens sounds like a gentle man with a lovely British accent, but the experiment does sound a touch sadistic.) He split the poor bastards into two groups:

Group A) While holding their hands in the freezing water, they said their favorite swear word over and over again, like a woman in labor.

Group B) While holding their hands in the freezing water, they said a neutral word over and over again, like “toothbrush” or “applesauce.”

Group A, the F-bombers, reported experiencing less pain. They were able to keep their hands under water 40 seconds longer than group B — roughly twice as long.

So how does this work? One theory is that taboo words are, inherently, more loaded with emotion than neutral words, and that they tap into a different chunk of the brain. “There’s indirect evidence that swearing isn’t associated with the cortex — where most language is — but instead taps into the deeper parts of the brain structure,” says Stephens. Profanity, therefore, is able to trigger our flight-or-fight mechanism, which can unleash adrenaline to help us tolerate pain or squeeze out a baby.

To buttress the theory that profanity is an emotional language, he then conducted an experiment to see whether our fluency with profanity changes in different emotional states. He recruited another batch of college volunteers. This time they played video games for ten minutes: One group played video golf, another played a violent first-person shooter. After the gaming, each student took a “swearing fluency test,” where you have one minute to write down as many swear words as you can. The control group (the golfers) only recorded seven, but the first-person shooters recorded eight. “That doesn’t sound like much,” admits Stephens, “but it’s statistically significant. In psychology, the difference between seven and eight is night and day.”

Of course I needed to know more about this swearing fluency test, which is clearly the best test ever. “People only got seven?” I ask. “That seems really low.”

“It’s harder than you think. People usually get five or six pretty easily, and then it really trails off.”

“What counts as a swear word?”

“You can say ‘fuck’ or ‘fuck-face’ or ‘fucking,’ but that’s just a variation of ‘fuck,’” says Stephens in his pleasant English accent — this was easily the highlight of my research. “So ‘fuck-face’ gets one point, but you can’t look around the room and say ’fuck-table.’”

Afterward I took my own swearing fluency test. I was sure I could pump out at least 20, maybe 30. I am not good at very many things in life, but swearing is one of them.

My score? Ten. I was so disappointed. But Stephens was right: It really is harder when you remove variants from the equation. For example, in my mind, an ass-clown is a harmless buffoon, whereas an ass-bag is more of a dick. (Go ahead and take the swearing fluency test for yourself — it’s a fun 60 seconds.)

The point is that our ability to use profanity is linked to our emotional state, an observation that squares with a 2011 experiment conducted by the University of Bristol, which found that it’s the swear words themselves, and not their meaning, that triggers an emotional response. The study hooked up volunteers to a machine that measured sweat levels, which is a proxy for measuring stress, and then asked them to say either actual swear words or their euphemisms.

People felt more stress when they said the taboo words … even when the meanings are identical. (In other words, your stress levels are higher when you say “fuck” than when you say “fiddlesticks.”) Taboo words have power. So while we roll our eyes at people who say “Oh, sugar!” instead of “Oh, shit!” there actually is a measurable, physiological difference in how the words are felt.

Or let’s take the most provocative and controversial word you know. Yeah, that one. In his stand-up act Chewed Up, Louis C.K. mocks TV reporters for going on air and saying “the N-word,” because we all know what that awful word means, and instead of using the euphemism, says Louis, you might as well just man up and say the awful word, because otherwise, you’re forcing the listener to fill in the blanks and say the actual N-word in our heads. I adore Louis, and it’s a clever argument, but since the taboo words themselves trigger more of an emotional impact than the meaning behind that taboo, in this case he might be mistaken. If I actually printed the N-word (which I will not do) you will physically feel worse than you do this second. For good or evil, substitute words just don’t pack the same punch.

Back to the benefits of swearing: It can help your career. “Profanity in the workplace can be a morale booster and inspire a sense of team spirit,” concludes a 2007 study from the University of East Anglia, as it can loosen us up and help break the ice. Then again … one person’s “loosening up” is another person’s “hostile work environment.” Just ask the former CEO of Yahoo, Carol Bartz, who once grumbled to Yahoo investors that there’s “nobody fucking doing anything” and once threatened her employees that she would “drop-kick them to fucking Mars.” After an ugly split with Yahoo she later said she regretted the profanity.

Too much profanity can dilute the impact. Another one of Stephens’s experiments found that “the higher the swearing frequency, the less was the benefit for pain tolerance.” If you abuse it you lose it.

So just like with almost everything, it comes down to fucking moderation.

Excerpted from THE GOOD NEWS ABOUT WHAT’S BAD FOR YOU… THE BAD NEWS ABOUT WHAT’S GOOD FOR YOU. Copyright © 2015 by Jeff Wilser. Excerpted by permission of Flatiron Books, a division of Macmillan Publishers. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.