Modern society provides us with all sorts of breath-freshening products: toothpaste, mints, mouthwash, gum, and even weird, translucent strips that dissolve in your mouth.

All these products have one thing in common: their default flavor is mint.

"The idea that mint equals freshness is an illusion"

By now, this seems quite natural. So it's hard to appreciate how interesting it is that Mentha spicata (spearmint) and Mentha × piperita (peppermint), a pair of shrubs native to Europe and Asia, have come to symbolize freshness for all of American society.

What's more, says cosmetics historian Rachel Weingarten, "the idea that mint equals freshness is more of an illusion than anything else. It's a triumph of advertising."

Peppermint does include menthol, which triggers receptors in your mouth that make it feel cold. But exclusively linking this feeling to our concept of "fresh breath" is pretty arbitrary — other countries, after all, have very differently-flavored toothpastes, such as clove and aloe.

So how did mint come to stand in for freshness? Here's the story.

A brief history of mouth care

"Our current use of mint is very a modern kind of thing," Weingarten says. In ancient history, spearmint and peppermint were mainly used as food and drink flavorings, or as medicines.

During the early Roman Empire, Pliny the Elder wrote that mint could be used as a remedy for 41 different ailments. Among other things, he wrote, it could be used to treat bleeding, liver disease, vomiting, and headaches. However, when it came to breath-freshening, this was his advice: "It is recommended to rub the teeth with ashes of burnt mouse-dung and honey."

for centuries, other plants were used to sweeten people's breath

For centuries, other plants and substances were used to sweeten people's breath. In the late 1700s, a French surgeon and dentist named Julien Botot introduced the first modern mouthwash, a fluid that contained gillyflower, ginger, and cinnamon, but not mint.

In the US and Europe, toothbrushing gradually came into fashion during the early 1800s, but for decades, people simply used water or abrasive powders while they brushed. To improve its flavor, some added crushed herbs — occasionally mint, but also things like rosemary, parsley, and sage.

Towards the end of the 19th century, a Connecticut dental surgeon named Washington Sheffield sold the first premixed toothpaste, and was quickly imitated by Colgate & Co. Both of their products contained some mint oil as a flavoring, but they also included other flavors. Neither was prominently advertised as mint — and at this point, the idea of "fresh breath" wasn't something commonly sold to consumers.

How mint took over

Two companies helped push mint to dominate the freshness market. Both relied upon marketers doing a very good job manipulating consumers to sell their products.

As Charles Duhigg writes in The Power of Habit, marketing executive Claude C. Hopkins was primarily responsible for making toothbrushing mainstream in the US. While pitching Pepsodent, introduced in 1915, he pushed the idea that the film on people's teeth — which they previously hadn't thought a ton about — was actually a big problem. Brushing them with Pepsodent would remove the film — and replace it with a clean, tingling feeling, the result of irritants like citric acid and mint oil (which contains menthol) in the paste.

Duhigg argues that Hopkins was exploiting the cue-routine-reward cycle, which research has since shown to underly the formation of all sorts of habits. Everyday, consumers would be cued to use Pepsodent by feeling the film on their teeth, and they'd be rewarded afterward by the tingling, which they'd come to crave.

Soon afterward, in the 1920s, manufacturers of Listerine — which had been introduced as a surgical antiseptic in 1879 — repurposed it as an over-the-counter mouthwash. To do so, they rolled out advertisements that prodded consumers to worry about another dire threat: halitosis.

"Listerine didn't invent the word halitosis, but they were very successful at making it a terrifying idea," Weingarten says. "They did a really good job building on insecurities."

Advertisements from the era tell consumers that halitosis is essentially social suicide — that it will scare off potential friends, business partners, and most importantly, lovers.

The campaign was a huge success, and Listerine sales exploded. The product itself generated a much stronger version of Pepsodent's cooling effect, but with a heavy dose of menthol, rather than mint.

In the ensuring years, competitors marketed all sorts of breath-freshening products — like Lifesavers — as cures for halitosis.

Though they mostly produced their cooling effect through menthol as well, mint became the flavor that got advertised — so much so that Lifesavers (sugary candies with mere traces of mint oil) became known as breath mints.

Mint's chemical secret

Mint originally became marketers' flavor of choice for a specific reason: peppermint includes menthol, a substance that interacts with receptors in our mouths to produce the sensation of cold.

It works like this: sensory neurons in your mouth (and elsewhere) are covered in a particular type of receptor called TRPM8. When these receptors get cold, they open up and allow ions into the neurons, which cause a signal to get passed up to your brain that tells you they're cold.

Menthol (and other cooling agents such as icilin and eucalyptol) produces the same effect, causing the receptors to open up even when temperatures aren't cold. Of course, this doesn't kill germs or mask bad breath any more than another flavor would, but that cooling sensation makes a big impression.

And the makers of Pepsodent, Listerine, and subsequent products have harnessed it to convince consumers that their breath problems are solved. Perhaps because mint (an attractive green shrub) is more appealing than menthol (a chemical that's now mostly made synthetically), the mint gets the attention.

Especially telling is the fact that in 1992, Listerine — the originator of the fresh breath idea, but with menthol, not mint — introduced a mint flavor of mouthwash. Put simply, we like the idea of mint more than menthol.

But what makes this really interesting is that the mouthwash, like many mint products, still produces the cooling sensation through menthol, and the mint taste wholly through artificial flavoring. In other words, it contains no mint oil.

"We love to believe in minty freshness, even though it doesn't really exist," Weingarten says. "If you're about to kiss someone, you want to feel like your breath is absolutely minty fresh. It's a wonderful illusion."