The pungency or heat of the pepper is a complex of seven closely related alkaloids or capsaicinoids. They often are called capsaicin, for the most prevalent compound. Capsaicin is a stable alkaloid that can be detected by human taste buds in solutions of one part per million. A subjective measure of chile heat, the Scoville Organoleptic Test, was invented by W. L. Scoville in 1912 and relies on trained tasters. A more objective measure of the amount of capsaicinoids present in chiles is measured by high-performance liquid chromatography.
People vary in their reaction to hot peppers.
The heat sensation from the capsaicinoids results from the irritation of pain receptors. People who repeatedly consume hot peppers build up a tolerance to the capsaicinoids and can eat very hot foods without a reaction. Habanero' and 'Scotch Bonnet' are cultivars of Capsicum chinense. Serrano' measures between 5,000 and 15,000. Mexi-bell' measures between 100 and 500 Scovilles.