The Scoville scale is the index for the heatness rating of peppers and ranges from 0 to 2.2 million Scoville heat units. The Scoville scale gets its name from its inventor, Wilbur Scoville, who worked as a pharmacist when he created the pepper index in 1912.
The index was created by getting a group of tasters to taste different chili peppers with sugar water to see how much sugar water was necessary to negate the heat of each pepper. Today, the heat of a pepper is easily measured by finding out how much capsaicin is in it. This chemical is the cause of the spicy heat in the chili peppers.
The scale assigns Scoville heat units, or SHUs, to foods as a unit of measurement. As of 2015, the two hottest peppers on the Scoville scale are the Carolina Reaper, at 2,200,000 SHU, and the Trinidad Moruga Scorpion, at 2,009,231 SHU. Some other incredibly hot chili peppers on the scale include the Komodo Dragon Chili Pepper, Naga Viper Pepper and the Infinity Chili. For comparison, the common bell pepper has an SHU of 0, while the jalapeño has an SHU of 1,000 to 4,000.