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.