Peaking at 2,200,000 Scoville units, the Carolina Reaper was named the world's hottest pepper by the Guinness World Records on August 7, 2013. As of July 3, 2015, that record still stands. Other notable contenders include the Trinidad Moruga Scorpion, the Bhut Jolokia and the Naga Viper.
Capsaicin is the chemical responsible for making chili peppers taste hot. The Scoville scale measures the hotness of chili peppers based on their capsaicin concentration. For reference, a bellpepper is rated at 0 Scoville heat units. Tabasco sauce typically ranges from 2000 to 5000 SHU, while Habanero peppers can reach up to 350,000 SHU.