Most home cooks know that the trick for tempering the heat of a chili pepper is to remove the seeds. The reason why it often works: Conventional wisdom holds that a pepper’s power is concentrated in the placenta—the central core of the fruit that contains the seeds, otherwise known as the pith—and the thick veins that attach the placenta to the pepper wall. Removing the seeds, then, usually results in removing the placenta and veins, thus cooling the fruit’s heat.

Another trick: Sometimes it’s possible to determine the heat of a pepper just by looking. Because capsaicin, the substance that makes chilis hot, is a yellowish liquid in its pure form, yellow veins often indicate more spice.  

“If you go to the grocery store, and, say, pick six jalapenos up, and cut them open and look at those veins, the more yellow you see, the hotter the jalapeno,” said Paul Bosland, a professor of horticulture and director of the Chile Pepper Institute at New Mexico State University.

Even when all those pieces are removed, though, some peppers—de-veined, de-seeded, and not yellow—still have a heat that just won’t chill, befuddling casual cooks and researchers alike.

For example, the ghost pepper, which doesn’t have many veins or appear particularly yellow, shouldn’t pack such a punch. But in 2007, Guinness World Records certified the ghost pepper as the world’s hottest chile pepper—some 400 times hotter than Tabasco sauce. (Pepper heat is measured in Scovilles, a unit based on the number of heat-producing alkaloids a pepper contains.)

It wasn’t until recently that researchers really understood the source of the ghost’s heat. One day last fall, Bosland and his colleagues were in the field cutting some ghost peppers when they noticed that the peppers walls were glistening in the sunlight. “Because the skin of the fruit is kind of a red-orange color, it’s sometimes hard to see that yellow vesicle. It just doesn't pop out at you like it does on the white placenta tissue,” said Bosland. The glistening made them think that perhaps the veins weren’t just along the interior placenta, but lining the inside wall of the fruit itself. Bosland took the peppers to Peter Cooke, who runs the electron microscope lab at New Mexico State University, to image it.

It turns out that capsaicin, the compound that gives chili peppers their fire, is well suited to fluorescence microscopy: Under the right conditions (think blacklights), it naturally glows in the dark. By giving the peppers the blacklight treatment, the researchers were able to show that though many varieties store the bulk of their heat in the center pith, some peppers work differently. They published their research in late 2015 in the Journal of the American Society for Horticultural Science.

Bosland and Cooke found that super-hot chili peppers—fruits that top one million on the Scoville scale—store as much heat in their fleshy skins as they do in the pith. In a jalapeno, if you remove the seed capsule, you slash the amount of capsaicin by roughly 100 percent—essentially all of the heat is in the placenta. But if you remove the veins and seed capsule from a ghost pepper, you reduce the amount of capsaicin by only 50 percent. In super-hot peppers, roughly half their capsaicin is stored in the skin. Stated plainly, super-hot peppers don't just have more capsaicin than chiller peppers; they store it differently.

“I’ve been saying that super-hot peppers are different for ten years,” said Ed Currie of the South Carolina based Pucker Butt Pepper Company. Currie breeds the Carolina Reaper, which at 1.5 million SHU claimed the title of the world’s hottest pepper in 2013. He’s also currently preparing to unveil a new pepper, currently titled HP56, which tops the Scoville scale at 2.2 million SHU—essentially with a bite as hot as pepper spray but in fruit form.

Currie can recite the health benefits of spice like a true pepper evangelist: The skin of super-hot peppers, he notes, has been studied for its cancer-fighting properties and effects on metabolism.

In fact, several studies in rodents and cells have found that capsaicin may help to fight cancers ranging from prostate cancer to colon cancer to leukemia. A 2015 study published in BMJ found that individuals who ate spicy foods almost every day had a 14-percent decreased likelihood of dying. Capsaicin is already a treatment for psoriasis and muscle aches—synthetic capsaicinoids are the key ingredients in over the counter muscle creams like Bengay.

Meanwhile, outside of medicine, the increase in super-hot peppers or peppers greater than 1 million SHU—in the ‘80s super-hot peppers were thought to max out around 500,000 SHU—has risen in tandem with the nation’s appetite for spicier foods.

“For many decades the United States, France, and Northern Europeans didn’t really eat spicy foods,” said Bosland. “When I first started working here people asked me if chili peppers were a fad. Nobody asks that anymore—it’s more mainstream.”

It’s a sentiment echoed by Gilbert Queeley, a research associate with  Florida A&M’s Cooperative Extension. Queeley works with farmers to help them find ways of increasing their profits from crops. Lately, that means scotch-bonnet peppers, which clock in at 100,000-350,000 SHUs, or 10 to 35 times hotter than the jalapeno. The increased demand and the scotch bonnet’s relatively high price—$2.75 to $3 dollars a pound, according to Queeley—means that some farmers can make significantly more money growing scotch bonnets than they can with other, more traditional vegetables.

“Most of the retailers around here and people in the hot-sauce industry were familiar with jalapeno peppers and Tabasco-type peppers, and for a while they stuck with what they knew,” said Queeley. “But once the Jamaican cuisine in particular started permeating throughout the south, and everyone got on the jerk sauce, and jerk seasoning, and jerk chicken bandwagon, the scotch bonnet pepper took off.”

And understanding the attributes that contribute to a pepper’s spice—like how capcaisin gets stored—makes it easier to breed peppers that meet demand, whether that’s medicinal or culinary.

Or both. Spice lovers say that the pain of eating a chili pepper is a draw, not a negative.  “With the chili heat, your body produces endorphins that make you feel better,” said Bosland. “You feel good when you eat it.”