Illustration of a woman holding up a pepper. In the background is a sea of chili peppers.

Credit: Dalbert B. Vilarino

Why do chilies hurt so good?

One JHU alum's obsession with chili peppers

For nearly 40 years, I've been gleefully setting my face on fire. It started when I was 9 or 10 and visited a farmers market with my mother. I spotted a display of cherry peppers, asked the vendor to try one, and bit in deep and hard. My reaction was instantaneous: cheeks turned red, and I began to sweat, pant, and salivate, an instinctively physiological response to relieve the overwhelming sensation of burning. It hurt, but I didn't want it to stop hurting. I was hooked.

In the decades since, I've consumed chilies in every form imaginable, from Thai curries to Oaxacan moles, Jamaican jerk to Sichuan hotpot. I've judged hot sauce competitions, farmed jalapeños and ají limon in my Brooklyn backyard, and speed chewed three Carolina Reapers—the world's hottest pepper, about 500 to 1,000 times as hot as a jalapeño—in an attempt at a Guinness World Record. (I failed.) Along the way I've tracked the 500-year journey of this fruit (yes, it's a fruit: genus Capsicum) from its origins in Central and South America to every corner and culture of this planet. What started as a foray into culinary masochism blossomed into full-on obsession.


Lately, however, I've been troubled by the very sensation that first snared me—by its falsity. What does it mean that we feel like our mouths are burning when we aren't in reality on fire? How are our senses fooled so completely? To get a better grasp on how, precisely, our bodies react to chili peppers, I called up Michael Caterina, a professor of neurosurgery at the Johns Hopkins School of Medicine, who was part of a team at the University of California, San Francisco, that in the 1990s uncovered exactly this mechanism.

At the time, research had shown that capsaicin, a compound extracted from chili peppers, targeted a subset of neurons that arouse or stimulate a nerve—or an organ—to activity. This subset is involved in the sensation of pain, like when you eat hot pizza too quickly and it burns the roof of your mouth. To find out how that was happening, Caterina, who earned his doctorate at Hopkins, went on a hunt for the genes responsible for programming those neurons.

His strategy: brute force, more or less. Using mouse and rat tissue, he built a system where he could feed sensory genes to their cells, then spritz them with capsaicin to see if any would light up. Problem was, he had 16,000 genes to test, in 130 different pools of cells. In pool No. 11, he saw a few cells light up. "I thought, that's interesting," he says. Caterina tried it again, got the same result. Waited a few days, got the same result. That's when he alerted the head of his lab, David Julius (a 2021 Nobel Prize laureate). After that, he said, "it was just turning the crank [to] find the one gene that could make the cells responsive to capsaicin."

The gene TRPV1—and the protein it creates—is one of six TRPV (transient receptor potential vanilloid) channels present throughout our nervous system—and the only one responsive to capsaicin. But why, Caterina wondered, is TRPV1 there at all? "We don't have capsaicin floating around in our bodies," he says, confidently. By torturing cells with an array of painful stimuli, Caterina and his team discovered that TRPV1 was designed to react to temperatures of 107.6 Fahrenheit and above. No wonder I turn red and start sweating, panting, and salivating.

In a way, it makes sense. Here's a gene tuned by evolution to generate a reaction to potentially dangerous temperatures and happens to get triggered by a chemical compound found only in a New World fruit.

What does it mean that we feel like our mouths are burning when we aren't in reality on fire? How are our senses fooled so completely?

Is that just a strange coincidence? Maybe. It depends on how you look at the genus Capsicum: Some scientists believe the plants evolved to produce capsaicin to ward off hungry mammals in favor of capsaicin-immune birds that could spread seeds far afield. Others see capsaicin as protection against bacterial and fungal pathogens. Me, I'm a "Why not both?" guy, although frankly, if Capsicum's goal was to keep mammals at bay, it has woefully failed when it comes to Homo sapiens.

For roughly 8,000 years, first in the Americas and for the last few centuries in the rest of the world, man has been eating chili peppers with gusto, and sweating, salivating, and smiling through it all. Not only that, but for 6,000 years we've been breeding them, crossing varietals to create ever spicier expressions, and giving them names that hint at danger: ghost, scorpion, reaper.

But why? What do we get out of hurting ourselves by activating an evolutionary warning system that's millions of years old? There's no hard-and-fast answer, but the explanations tend to fall into two categories: biological and cultural.

On the biological side, we have endorphins—essentially, the chemicals your body releases to make you feel good, or at least better, in response to painful stimuli, like eating chilies or running long distances. A 2021 paper by a team of Dutch scientists offered a computational model of this pain-pleasure cycle, considering how, over time, a spicy food lover becomes desensitized to certain levels of capsaicin, craving ever-spicier delights. The more we hurt, the better we feel, and the better we feel, the more we crave the hurt.

The cultural side is messier. In countries whose cuisines are not particularly spicy, it's a badge of honor to be able to eat extremely hot foods: When I vied for that Carolina Reaper–eating world record, it was onstage in front of hundreds at a hot-sauce convention, and for an hour afterward people came up to congratulate me. But in places like Jamaica, Thailand, and India, where powerful chilies are just another flavoring, there's nothing special about tolerating spice—it's simply food.

How and why you enjoy spice can even depend on your gender: A 2015 study found that while men liked chilies for the social reward—approval by their peers—women liked chilies for the sensation itself. Is that culture or biology? Like I said, it's messy.

For Steven Gross, chair of the Hopkins Philosophy Department, who works on issues of mind and language and the foundation of the mind-brain sciences, the question of why we like chili peppers—and other acquired tastes like beer or Taiwanese stinky tofu—is partly about how humans exploit the way their brains misperceive reality. That is, we taste dangerously high heat in chilies, potentially poisonous bitterness in beer, and seemingly deadly putrefaction in stinky tofu, and yet we survive, and because we survive, we take pleasure in fooling our brains again and again.

We do likewise, Gross pointed out, with optical illusions. (Are those lines the same length? Is the dress black and blue or white and gold?) Instead of discovering a bug in our code and doing everything in our power to avoid triggering it, we humans tend to poke and prod, to find ever more creative ways to trick ourselves, both for the pleasure of the disjunction and to understand its origins. Evolution, too, has led us to this point, gifting us glitches in our collective matrix as well as the programming, or metacognition, or sheer perversion that allows us to find delight in getting things wrong and right at the same time. Even if you're just a brain in a vat of hot sauce, there's joy to be had.

Matt Gross, A&S '96, '98 (MA), is a Brooklyn-based writer and digital media strategist. He is (very slowly) working on a book about the history of the chili pepper.