Chemically, capsaicin is corrosive (like hydrogen peroxide), acutely toxic (like chlorine), and irritating (like ammonia). And its irritant qualities won’t just fire up your mouth: Capsaicin can have a similar effect on other mucous membranes. If you’ve ever chopped peppers and then accidentally touched your eye, you understand how irritating this compound can be. 

So why do some people enjoy—and even get a thrill out of—eating a fruit with such a kick?

“We get interviewed often by chiliheads,” Guzmán says. “I’m Mexican. I grew up eating jalapeños, I grew up eating really spicy food, and I understand that there are other chemicals in [peppers] that are medicinal. But when it comes to chiliheads, I think they’re fascinated by the chemistry of capsaicin and how it makes you feel something you’ve never felt before. It gives you a euphoria.” 

Measuring that euphoria depends on the Scoville scale.

Let’s talk Scovilles

Named for American pharmacist Wilbur Scoville, the Scoville scale ranks the pungency of chile peppers based on the concentration of capsaicin in the pepper. It’s this concentration that determines how our bodies will react to peppers; while small amounts of capsaicin fall within the “spicy chicken dinner” category, stronger concentrations spell out “weapon-grade pepper spray.” 

In the early 1900s, Scoville, who was working as a chemist at the time, attempted to test out people’s relative capsaicin tolerance. He recruited five human subjects to taste-test mixtures of dried pepper and sugar water and had them report how hot they found each mixture to be. The basis of his heat scale is the amount of sugar water needed to dilute the mixture enough for the majority of his subjects to no longer feel the heat. 

These days, a technique called high-performance liquid chromatography is used to determine exactly how much capsaicin a pepper contains in parts per million, and multiplying the result by 16 converts it to Scoville Heat Units (SHUs).

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The highest level of naturally occuring capsaicin is in the Carolina Reaper, the hottest pepper in the world. Its creator, chile pepper grower Ed Currie, bred the pepper by taking one uniquely spicy habanero grown on the La Soufrière volcano on Saint Vincent in the Caribbean and crossing it with a Naga Viper pepper, which was developed in the United Kingdom from peppers hailing from the Caribbean and South Asia. The hottest single Carolina Reaper ever to be harvested rang in at 2.2 million SHU, meaning that more than a tenth of the pepper was pure capsaicin.

High amounts of capsaicin, like those found in the Carolina Reaper, can cause injury. “Capsaicin is a really potent chemical. If you have too much of it, it can be toxic,” Buckley says. “It’s the thing that’s used in pepper spray. We’ve all seen images of people who have been pepper sprayed. Their eyes are swollen up, they’re crying, they can’t see…so it’s incredibly important to know how to handle capsaicin” safely, she says.

Your body’s battle against spice

If you don’t welcome spicy burns, there’s a way to neutralize the compound’s effects: dairy. “Capsaicin is an oil and it is insoluble in cold water,” Buckley says. Though it’s somewhat soluble in alcohol, like beer, Buckley explains, capsaicin is best dissolved by another oil. “You need to find something that’s fatty to dissolve the capsaicin,” she says. “That’s why the best thing to drink is milk.” 

Although spicy food is sometimes associated with stomach problems—Currie, who not only created the Carolina Reaper but also eats one every day, still experiences severe stomach cramps—there is no direct evidence that spicy food causes belly cramps or nausea. The perceived pain, Guzmán explains, may just be a side effect of your gut membranes being irritated. While a 2016 study showed capsaicin can cause those with abdominal disorders to experience flare-ups in their symptoms, the same can be said for too much bread, a famously unspicy food.

But there are always worst-case scenarios.

Trinidad scorpion pepper

A Trinidad moruga scorpion pepper, which is currently the second hottest pepper in the world to the Carolina reaper. Image credit: John Vonderlin, Flickr

More than 150 different varieties of chile grow in a garden at New Mexico State University’s Chile Pepper Institute. “One year we had a group of students we were doing a tour with in the garden. And one student thought it would be funny if he bit a tiny piece off a Trinidad Scorpion pepper,” Guzmán says. “He did that, and he threw up in the garden, and he passed out, and we had to carry him to a shaded area under some trees.” 

Because capsaicin is a toxin, Guzmán explains, the human body’s first response to an excess of it is to flush it out. (In the student’s case, by vomiting.) 

In 2018, the National Institutes of Health reported that a previously healthy 34-year-old man was admitted to the hospital with “thunderclap headaches”—sudden, severe head pain accompanied by fever, blurred vision, and even seizures—after eating a Carolina Reaper whole. Doctors treated him by flushing the capsaicin out of his body, which, like many chemical compounds in large amounts, can be dangerous. 

Of course, Olympic equestrian Tony André Hansen’s story shows that even a small amount of this complex compound can be damaging (and in some cases, even career-ruining). It just depends on where—or upon whom—the capsaicin ends up.

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