Why do chillies burn?
Professor John Miller, School of Biological Sciences, discusses Chillies and their heat.
Chillies burn because they contain a substance called capsaicin that stimulates temperature receptors in the body.
These receptors respond directly to heat. Thus the brain interprets the chilli substance activation of the receptors as a burning sensation. A genetically related receptor responds to cool temperatures, and in addition to cold, this receptor also responds to menthol, hence, the cooling sensation of menthol mints or sprays. Intense cold can also give a pain sensation because of the activation of this family of receptors.