It’s the question that starts fights among hardcore chiliheads: Which hot pepper brings the heat—as in BRINGS IT?

That leads to a Chili 101 question: How do you measure hot pepper heat?

The answer to that question is straightforward.

The Scoville scale, named after creator Wilbur Scoville, measures pepper pungency in Scoville Heat Units (SHU) on scale from 0 (your average sweet pepper) to, well, lots (anything over 80,000 is considered “very highly pungent”…but as we’ll see, that’s just a jumping-off point).

That heat comes from compounds called capsaicinoids, the most prominent (and best known) of which is capsaicin.

Despite its science-y sound, the Scoville scale is actually based on a subjective assessment: how much sugar water is needed before someone sampling hot peppers doesn’t detect any pungency whatsoever.

“Pungency is a complex trait,” says biochemist Johnna Roose, PhD, who blogs at New Under the Sun. And while she gives due credit to genetics—in particular a gene called Pun1, which cranks up capsaicin production—she also notes that “the environment has a significant impact on how spicy the harvested peppers will be.”

Roose says the key to getting a really hot pepper is stress, such as lack of water or high temperatures, which “tends to increase pepper pungency.” (For home gardeners, that means stressing the plant once the peppers start to develop, as well as not over-fertilizing with nitrogen and letting the peppers age fully on the vine.)

Some of the most popular “hot” peppers don’t come anywhere near the list of hottest on the planet.

That includes the Jalepeño, which peaks at 8,000 SHU and averages 5,250; the Serrano, which averages 16,500 and peaks at 23,000; and your garden-variety Habanero, which clocks in at 225,000 on average and 350,000 at peak.

Even the famous Ghost Pepper doesn’t claim top spot on the following list, which comes from Pepperhead.com.

1. Carolina Reaper (2,200,000 peak SHU)

“It was bred for heat,” say the folks at Pepperhead.com, noting that the Reaper “is 200x hotter than a jalepeño” and adding that it has “excellent fruity flavor to boot. Well, that is before it melts your face off.”

2. Trinidad Moruga Scorpion (2,009,231 SHU)

“Once you take a bite of this formidable pepper, the heat never stops building,” say the Pepperhead folks.

3. 7 Pot Douglah (1,853,936 SHU)

“The hottest ‘superhot’ peppers are traditionally red,” notes Pepperhead, “but the Douglah defies the odds by being brown and scorching hot.”

4. 7 Pot Primo (1,469,000 SHU)

“When you just look at this pepper, you know it’s going to be insanely hot,” says Pepperhead.

5. Trinidad Scorpion “Butch T” (1,463,700 SHU)

Pepperhead notes, “The burn from this pepper is unlike any other.”

6. Naga Viper (1,349,000 SHU)

“Naga Viper is an extremely rare pepper cultivated in the UK,” says Pepperhead. (The UK doesn’t seem to be a natural fit for hot peppers, but we digress.)

7. Ghost Pepper, aka Bhut Jolokia (1,041,427 SHU)

Here it is! Pepperhead explains that the Ghost Pepper’s fame comes from “YouTube and other social sites where pepperheads ate whole Ghost Peppers as part of a challenge. This is the first pepper to scientifically test over 1 million Scovilles.”

8. 7 Pot Barrackpore (around 1,000,000 SHU)

“This one is from the town of Chaguanas in Trinidad and Tobago,” says Pepperhead. “Many of these ‘super hots’ come from this region.” (We’ve noticed.)

9. 7 Pot Red (Giant; around 1,000,000 SHU)

“The ‘7 pots’ were named after their ability to heat up seven pots of stew,” explains Pepperhead.

10. Red Savina Habanero (500,000 SHU)

“Back in the early years of super hots, the Red Savina Habanero was king!” say the folks at Pepperhead. Now this variety “just barely makes the Top 10, but does so in fashion with its great flavor and extreme heat.”