The spice that has the most capsaicin is the Pepper X chili pepper.
The Pepper X chili pepper is the hottest known pepper and spice with a world record heat of 2.69 million SHU or Scoville units.
The Carolina Reaper pepper is the next hottest spice and hottest pepper.
The Carolina Reaper pepper has a heat rating of around 1,641,183 SHU or Scoville Unites.
For comparison, a Jalapeno pepper is usually around 10,000 SHU or Scoville Units, which makes the Carolina Reaper pepper, over 100 times hotter than Jalapeno peppers.
The Apocalypse Scorpion Pepper is around 1,400,000 Scoville heat units.
Capsaicin levels are measured in Scoville Heat Units or SHU, with hotter peppers containing more of the compound.
Capsaicin is the chemical compound in chili peppers and hot peppers that is responsible for the heat, which acts as a natural irritant, which also stimulates the pain receptors in the body, but eventually desensitizes them and makes it useful in topical creams for pain relief such as muscle soreness and arthritis and for use in sprays as a deterrent for bears and pests.
The capsaicin in hot peppers and chili peppers also can benefit your health by boosting your metabolism, but can also cause digestive upset, nausea or even heart burn and it's effects also vary from mild warning to intense burning.
The capsaicin and several related amides or capsaicinoids are produced as a secondary metabolites by chili peppers, which are likely as deterrents against eating by mammals.