The delicious burn of a really good curry or salsa or Sichuanese hot pot – that fiery goodness that makes you sweat and flush – is for many people one of life’s great pleasures. The search for the most profound scorch is a hobby of sorts, perhaps even an obsession.

And hot-hunters are safe in the knowledge that although capsaicin, the spicy molecule in hot peppers, is activating receptors in pain neurons in their mouths, it’s not really causing any damage. Give it a few minutes, and the feeling that you’ve torched yourself will fade, only returning when the meal – ah – leaves the premises, a day or so later. It’s all fun and games. Right?

Well, until someone gets hurt.

Chillies are rated on a spiciness scale known as Scoville – a grading of heat that goes from the lowly bell pepper (0) right up to the fearsomely named Carolina Reaper (2.2 million). And while everyday amounts of spicy food are unlikely to do any harm, thrill-seekers have had some disconcerting experiences. In 2014, two journalists from The Argus, a newspaper in the British city of Brighton, went to test out burgers at a local restaurant rated highly on TripAdvisor. They each took a bite of the XXX Hot Chilli Burger, a specialty of the house made with hot sauce touted by the owner to score higher on the Scoville scale than pepper spray.

The pain was unendurable – one reporter immediately swallowed a great deal of milk to try to stave it off, the newspaper reported. The other began to have severe stomach pains, lost the feeling in his hands, and began to shake and hyperventilate. His colleague was also seized with pain despite his efforts, and both had to go to the hospital. “I was in so much pain,” one said, “I felt like I was dying.” (Read the whole story here.)

Daring pepper eaters who consume some of the world’s hottest specimens on camera have found themselves vomiting for an audience. A miniature YouTube film festival of hot pepper eating and its regurgitatory consequences is a rivetting spectacle, writes Aaron Thier for Lucky Peach, who describes a slowed-down recording of a Danish event where a thousand people ate ghost peppers. “Everyone sweats and hiccups, as usual, but the editing gives it a mythic, eternal, lyrical quality. The vomiting seems exultant,” he writes.

Matt Gross’s account of hot debauchery for Bon Appetit, on the other hand, starts with the cold, hard numbers. “It took me 21.85 seconds to consume three Carolina Reapers, the world’s hottest chillies. And it took me approximately 14 hours to recover from the aftermath,” he says. (Spoiler: The aftermath involved the symptoms of a heart attack.)

The physical effects of eating peppers can be seen as reactions to what might be – from the body’s perspective – real burns

So what is going on here? If all hot peppers are doing is fooling your body into thinking there’s a small fire in your mouth, why can they provoke such a serious reaction?

Let’s come back to the basic biology of capsaicin. This molecule may have evolved as an anti-fungal agent for the plants that bore it. But, to humans’ joy and fascination and fear, it happens to activate certain neurons responsible for the perception of pain. Those particular neurons send a message of heat to the brain, whether the cells are activated by an actual burn or by a hot pepper. It’s not their business to distinguish between these noxious options – as far as the body is concerned, it’s better safe than sorry.

The physical effects of eating peppers can be seen as reactions to what might be — from the body’s perspective — real burns, says Bruce Bryant, a biologist at the Monell Chemical Senses Center in Philadelphia. Sweating is an adaptation for cooling off. Triggered pain neurons release substances that cause blood vessels to widen, resulting in inflammation, the better to supply the damaged area with blood and the body’s first responders.

When that Carolina Reaper hits your stomach lining and you retch, “that response is because there are pain-sensing nerve endings in the stomach”, says Bryant. “The body says, ‘I don't care if it’s a thermal burn or a chemical, but I’m going to get rid of it.’”

Very serious discomfort aside, there don’t seem to be long-term dangers, per se, in eating very hot peppers

The responses that your body might have if you’d swallowed a caustic substance come into play with high levels of capsaicin because that is, after all, what the molecule mimics. Those burn-sensing neurons, in your mouth, stomach, and elsewhere, are going to do their thing whether what you’ve swallowed will really kill you or just give you some discomfort on the toilet.

But, hours or a day or so of very serious discomfort aside, there don’t seem to be long-term dangers, per se, in eating very hot peppers. Biologists have observed, however, that administering capsaicin over long periods of time in young mammals does result in the death of the pain neurons, Bryant says. Setting the neurons off repeatedly wears them out, and they don’t grow back.

Interestingly, there is even a theory that pepper plants might have developed the molecule as a way to deter mammals from chewing up their seeds. Birds, which eat pepper seeds whole and helpfully spread them in their faeces, do not have the necessary receptors to feel the burn. But in humans, pepper plants have encountered a special kind of mammal that courts the feeling, to the edge of reason and probably a little bit beyond.

Luckily for the pepper, this does not seem to have damaged its fortunes.

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