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I am tearing into some Chinese takeout today for the sake of science. These are the goods we got from Panda Gourmet. Oh, my God. This looks great.

Ask anyone in D.C. - Panda Gourmet is an institution, a Chinese restaurant affixed to a Days Inn off a highway with a replica of a Xien terracotta army warrior out front. Their food is known for being authentic, delicious and, yes, spicy.

This is fish fillet with silk tofu in hot chili.

RUTH TAM, BYLINE: This is, like, one of my favorite dishes of all time.

KWONG: My dinner guest is Ruth Tam, a D.C.-based food journalist and co-host of "Dish City," a podcast looking at city change through the region's iconic dishes and cuisines. Ruth grew up eating Cantonese food in the Chicago area, but it wasn't all that spicy. She really got into spicy food when she moved to the district, though she's not the type to smother hot sauce on a dish just because.

TAM: Eating spicy food doesn't have to be, like, a competition, but so often I feel like spiciness gets used as, like, shorthand for how, like, tough you are and also, like, how culturally authentic something is. And I think that that's, like, so off-base.

KWONG: And yet, from the celebrity web series "Hot Ones" to condiments with names like California Reaper Rectum Wrecker, we treat spice like a badge of honor, even though, scientifically speaking, it is inducing in our bodies a pain response.

TAM: And I am curious if there are, like, different personalities that are drawn to spicy food and, like, why some people seem to be so sensitive to spicy food and others are able to build up their tolerance or maybe don't even have to build up a tolerance - they just can handle it.

KWONG: Today on the show, we answer Ruth's question. What's up with humans and spicy food? We are one of the very few known mammals in the world to deliberately seek it out. But why? We talk to scientists about what drives spicy-seeking behavior and what research suggests about whose personalities are reaching for the horseradish and habaneros the most. I'm Emily Kwong. And you're listening to SHORT WAVE, the daily science podcast from NPR.

KWONG: Let's dig into this.

So over a picnic blanket, with Pepcid on hand, Ruth and I dive into the spiciest food on Panda Gourmet's menu and trade opinions about the heat using the very scientific methodology known as, on a scale of 1 to 10 - 10 being inferno, I want to die, one being, meh, shrug emoji. We start with the shannixi cold-steamed noodles, pouring half a serving of chili oil on top.

TAM: So squishy and delicious.

KWONG: It's so doughy. Oh, this is so yummy. I would consider this heat, like, pleasant and pretty...

TAM: We could probably do a little more.

KWONG: ...Pretty mild. Should we just go for it and put it all in?

TAM: We'll have to find out.

So in goes the entire container of chili oil, and I suddenly feel a pleasant sweat percolating. For Ruth, the noodles are a six - for me, a four. So we up the ante, breaking open that fish fillet with silk tofu floating in a bath of electric-red chili oil.

Oh, no, it's actually spicy. Oh...

TAM: That was so fast.

TAM: Did you take a bite?

KWONG: No. My chopsticks were dipped in the sauce, and I felt an actual burning sensation.

OK, in my defense, spice is like this sometimes. Right? A dish that sets one person's tongue aflame is another person's no-big-deal. Ruth and I agreed this wasn't the spiciest food we'd ever eaten in D.C. and that our reactions to a truly hot dish induces a feeling unlike any other.

TAM: Like, your lips get tingly. They maybe swell. Like, your mouth is starting to, like, heat up, and you maybe start crying. Your face gets red, and all of a sudden you're, like, sobbing and, like, dry-heaving over a table. And, like, it legitimately is, like, an allergic reaction. And it's one that people seek out.

KWONG: And it's one that fascinates Julie Yu.

JULIE YU: Your brain doesn't actually know the difference between eating capsaicin and touching something hot, and that's why we have the same physiological response.

KWONG: Julie is a senior scientist at the Exploratorium, a museum of science, art and perception in San Francisco. And she says, it's the receptors in our bodies that are responsible for our ability to sense spice, converting an encounter with, say, the compound capsaicin found in chili peppers into electrical signals.

YU: And so there's a three-dimensional fit between the squirrely blob that's capsaicin and the squirrely blob that's your receptor. And what happens when capsaicin binds to that receptor is it triggers a chain.

KWONG: A chain of reactions that travels along our trigeminal nerve, which helps your face recognize pain and touch sensations, as well as heat and cold. Your brain registers spiciness as actual burning. The exact same receptors are activated when you, say, take a sip of soup that's too hot temperaturewise. And Julie points out, this is cutting-edge science. The Nobel Prize in medicine last year was awarded to physiologist David Julius, who identified the very gene that allows our cells to detect heat. And he did this by hacking the same compound in your Tapatio hot sauce - capsaicin. And that is why the response is the same - sweating, nose running, eyes watering.

YU: Your brain has been told there's a potentially dangerous stimulus and we need to clear it out.

KWONG: This is true of capsaicin. And it's also true of the molecule found in mustard and wasabi and horseradish - allyl isothiocyanate. That binds to the same receptor as capsaicin, and it also binds to a second receptor that's triggered by airborne irritants.

YU: This second receptor, and in the same family, is sensitive to tear gas or car exhaust or other things that might make you cough.

KWONG: So when you eat horseradish or wasabi, it's giving you a burning sensation and causing you to hack up a lung. And that's because allyl isothiocyanates tend to go from liquid to air more readily.

YU: They flood your nasal passages, and your brain thinks that there's an airborne irritant. You know, all of a sudden your sinuses draining, and you cough, and you get this flash of a different sense of spiciness.

KWONG: Even just you describing it, I really don't like that.

YU: Yeah, I mean, I as well.

YU: I think it's definitely informed by what I grew up with. I grew up eating much more capsaicin.

KWONG: This isn't the case, though, for Nadia Byrnes.

NADIA BYRNES: I'm Ukrainian. I grew up eating horseradish. I grew up eating mustard. Like, it is - that is my preferred spice of choice.

KWONG: Nadia is the sensory science manager at Ocean Spray Cranberries. And back in the day, while earning her Ph.D. at Penn State, her dissertation focused on how personality and experiential variables impact liking spicy food, which Nadia adores.

BYRNES: My Ph.D. adviser always liked to joke that I was born to study this because my name is Dr. Byrnes. For me, enough is when I get a moment of blackout, and my whole head kind of goes whoosh.

KWONG: Nadia points out that we are the only known mammals, aside from this one tree shrew, that deliberately seek out spicy food. She wanted to know why. If spice is inherently painful, why do we dig it? And why do some people dig it more than others? Well, there are genetic variables that can impact your baseline sensitivity to spiciness. The rest is driven by your personality and life experiences. In the 1980s, cultural psychologist Paul Rozin laid the groundwork for this connection. He was the one to theorize that there's a correlation between liking spicy food and being a thrill-seeker.

BYRNES: It was a very general correlation. And so, you know, that would suggest that somebody who likes spicy food is more likely not only to enjoy public speaking and maybe skydiving, but also doing things like speeding and, you know, illicit drug use.

KWONG: But Nadia and her Ph.D. adviser, John Hayes, thought there's got to be more to the story. They both loved the burn of spicy food, but they didn't consider themselves risk-takers.

BYRNES: Is it really that being a spicy-food-liker makes you more likely to engage in all of these risky behaviors, or are there certain patterns that are more strongly exhibited than others?

KWONG: And to figure that out, Nadia used a battery of personality metrics in her dissertation. One of them used in the final study was something called the balloon analogue risk task. She asked subjects to press a button to inflate a balloon on a screen, and every time they inflated the balloon, they earned money.

BYRNES: And if the balloon pops, you lose everything that's in your temporary bank. And people did walk out the door with, you know, money, so there was actual money on the line. And we're working with college students here.

KWONG: What were you trying to measure in that moment?

BYRNES: So what we were trying to do was to parse out risk-taking, sensation-seeking and sensitivity to reward.

KWONG: So sensation-seekers are people who tend to seek out novel sensations - not all of the sensations in the world, but some of them. And sensitivity to reward tends to predict how you react to things that are considered important in your culture. So people with a high sensitivity to reward tend to have a greater affinity for social approval or status or money. And that tends to correlate to a person being a bit more impulsive. So with these ideas in mind, Nadia ran this balloon test on over 100 participants, all of whom she pre-fed strawberry jelly laced with capsaicin, so she would know their spice tolerance. And she found something interesting. Those in the study who liked spicy food did tend to be sensation-seekers. But their experiences differed slightly by gender. Women liked the sensation, the novelty of the spiciness itself, whereas men who liked the burn tended to also be more sensitive to those social rewards. And that kind of tracks with what Ruth Tam said earlier about spiciness being a competition. Here's Nadia.

BYRNES: The society that we exist in often tends to reinforce that eating spicy foods is a macho behavior, or it's some sort of indication of strength. And so it's kind of this reinforcement loop.

KWONG: So at the end of the day, Nadia found that those who have a higher sensitivity to reward are also more likely to enjoy spicy food. And if you're not one of these people, we have good news for you. You can learn how to eat and enjoy spicy food. You can allow your brain and body to grow more desensitized. Here's an example. Have you ever cranked the music on a song in your car, and after a while, it just doesn't feel as loud anymore? And then you turn it on later, and it's suddenly way too loud? You can apply that same logic to hot pot.

BYRNES: The brain is a weird and wonderful thing. And so sometimes our brains will essentially turn down the volume on something that is annoying or painful or whatever it is.

KWONG: Which can be done by eating a little more spicy food each time and a little more frequently. You don't have to push yourself to the breaking point. Your brain will turn down the volume on that sensation over time.

Girl, this is hot. I don't know what you're talking about.

TAM: Like, it's basically faded from my mouth, like, the memory of that spice.

KWONG: You're showing off now.

KWONG: I don't know what to tell you.

TAM: But now try the tofu because I'm curious.

KWONG: In the end, Ruth and I did not need the Pepcid, nor the milk our producer Thomas Lu kindly offered to buy, which, if we had, would have been useful because milk contains casein, a molecule that surrounds the capsaicin and washes it away so it won't bind to as many receptors and wreck as much havoc on your dignity. What's interesting is that as potent as spice is, it's not considered one of the five classical tastes. And that's because spice triggers pain, and that's processed very differently than taste in our bodies. Our bodies have pain receptors all over the place, not just in our mouths, which is why, as far as stories go, a spicy meal tends to have a beginning and an ending.

YU: Hi. This is Julie Yu. I'm recording a follow-up answer to a follow-up question about why we might detect spiciness in our poop. And my response is the receptor that detects capsaicin is really present all over our bodies, including at both ends of our digestive system.

KWONG: Spicy food - so good you feel the burn twice.

KWONG: This episode was produced by Thomas Lu. It was edited by Stephanie O'Neill and fact-checked by Rachel Carlson. Special thanks to Mei Lai and Panda Gourmet in Washington, D.C., for the takeout and to Mia (ph) the dog, who kept Nadia's toes warm while writing her dissertation. Gisele Grayson is our senior supervising editor. Andrea Kissack is the head of the science desk. Beth Donovan is our senior director. And Anya Grundmann is our senior vice president of programming.

I'm Emily Kwong. Thanks for listening to SHORT WAVE, the daily science podcast from NPR.

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