Once, and only once, I saw a stranger behaving curiously in the toothpaste aisle. He was standing with his arms crossed and brow furrowed; his eyes seemed to scan everything from the top shelf to bottom, then back to the top again. I waited some time for him to move before I realized that he was doing the same thing I had come to do: Read the labels and frown. Cool Mint, Strong Mint, Radiant Mint, Fresh Mint, Clean Mint, Vanilla Mint, Spearmint, Cinnamint, Now With Intense Mint Flavor: There were no options without mint.

I can’t speak for the stranger, but my disappointment with this stunning variety was dermatological. In my early 20s I was diagnosed with a skin condition that was aggravated by among other things, mint oil. At the time, I was a serious mint user: I always had a pack of gum in my bag and thought Altoids were a required final course after every meal. I replaced the breath mints with xylitol-based fruit gums and the old-fashioned remedy of fresh fruit after a meal, but mintless toothpaste is a specialty item, difficult to find: for most toothpastes, mint is an essential feature, not an optional flavor.

But in the history of dental hygiene, the ubiquity of mint is a relatively recent phenomenon. Humankind has devised itself breath fresheners and dental abrasives throughout recorded time, but these varied greatly among cultures, depending mostly on what materials were available. Crushed shells, chalk or brick dust, and even powdered bone could serve to scrub teeth and clean the gums until the invention of toothpaste in the late 19th century. To sweeten the breath, medieval Europeans could crush herbs into their tooth scrub or vinegar mouthwash; mint was sometimes used for this purpose, but so were rosemary, parsley, and sage. Other cultures chewed aromatic seeds — fennel seeds, cardamom, star anise — to abrade and sweeten the mouth; some of these fragrant seeds still appear in the bowls of colorful mukhwas you see at Indian restaurants.

The twentieth century brought several changes to this homemade, all-natural dental care: improved science led to a better understanding of hygiene and new technology led to the industrialization of materials that had previously been made in the home, as well as brand new products. One of these products, Listerine, made good use of another twentieth-century device — advertising.

The Listerine company didn’t invent halitosis — neither the word nor the condition — but they did invent an extremely effective marketing campaign for an extremely foul-tasting liquid. Originally a surgical antiseptic, Listerine destroys the primary cause of malodorous breath, bacteria that live in the mouth. But science aside, the acrid antiseptic won its way into the mouths of the American public by way of social insecurities. No one wants bad breath, and if everyone else is gargling with Listerine, then those who don’t will become social pariahs.

A campaign like this, which exaggerates a social ailment and normalizes the cure, can rewrite cultural history. Suddenly, daily mouth care was considered the new normal, a recognizable routine that other products could capitalize on. This 1932 Lifesavers ad not only draws a character from Listerine’s campaign, reanimating the halitosis-suffering social and romantic outcast, but it also builds on the normalized practice of mouthwash. It’s not enough to rinse the mouth, claims the ad; you should be ready to pop a breath-sweetening candy throughout the day.

There’s not a single ingredient in a Lifesaver that combats halitosis or cleans the mouth, but each of the candies offered in this ad features a flavor agent that has historically been used as a breath freshener: Pep-O- mint, Wint-O-green, Cl-O-ve, Lic-O-rice, Cinn-O-mon, and Vi-O-let. Violet and licorice seem like old-fashioned flavors to us now, but both have sweet and slightly astringent tastes made them good crossover candies for a breath-saving sweet. Clove and cinnamon still appear in toothpastes today, particularly European and Middle Eastern brands, thanks to their strong and fiery flavors. But for an early twentieth century American manufacturer, mint oils would have been the cheapest and easiest breath-freshening flavor agent to obtain. Mint farms flourished in cool, damp regions near the Great Lakes and in the Pacific Northwest; some companies had already made a fortune distilling mint oils for export and medicinal use (peppermint was thought to use digestive distress), and the addition of the manufacture of candies and toothpastes was a lucrative leap.

But it wasn’t accessibility alone that made peppermint the most popular Lifesaver flavor for years and, over time, the preferred flavor for dental hygiene products. It’s the sensation, more than the scent or the taste, that causes us to associate mint with clean mouths. Mint makes the mouth feel cold.

That “fresh” sensation is a thermal illusion: the actual temperature of your mouth doesn’t change. Mouths contain particular cells that that activate in the presence of hot or cold: the condition of extreme temperature “turns on” the cell, which then sends a message to the brain that the mouth is rather hot or rather cold. But menthol also “turns on” these cells, which send their message to the brain as directed, and we experience a coolness in the mouth that isn’t there. By itself, mint doesn’t make the mouth a less suitable environment for germs; it’s the abrasives in toothpastes or the alcohols in mouthwashes that do the dirty work. But it’s easy to see how minty freshness became associated with cleanliness: the illusory change of temperature and the sharp, distinctive taste remind us more of cleaning agents than candy.

At the same time, the cool feeling of mint is more appealing and marketable than the taste of actual astringent solutions. Classic Listerine doesn’t cool, it burns: that fiery sensation is not a thermal illusion but a mild irritation of the sensitive mouth tissues as the antiseptic solution goes about its germ-killing business. Effective, but it doesn’t make a strong case for its own daily use. And so, in an intriguing reversal of the invented demand for antiseptic mouthwash, the market compelled Listerine to introduce a gentler, mint-flavored antiseptic for the first time in 1992. As the company president remarked to the New York Times, they’d done their research, and they knew that mint is what the market wanted.

In the toothpaste aisle, it certainly seemed that other dental care companies were acting on the same research, deviating from mintiness only for children, who perhaps haven’t yet acquired the taste for the strong, astringent flavor. Adult toothpastes tend to come with a maximized mint punch. Because we associate that cool sensation with a clean sensation, toothpastes promise us more intense mint flavor to create the illusion of a more intensely clean mouth.

The promise is not so appealing if you associate mint oil with a puffy, swollen mouth and itchy face, however. My mint reaction subsided as I got older, as often happens with allergies, so I now enjoy mint tea and can withstand a mildly minted baking soda toothpaste. But without the daily exposure to concentrated mint oils, the tastes of “mint expressions” and “curiously strong mints” are repellent to me. • 12 November 2012