Chillies are spicy vegetables that are hot to taste and come in different levels of heat. There are many ways to distinguish each variety of chilli seeds by heat and the one that is used in all countries is by measuring the heat of the chilli seeds by the Scoville scale. This is a measurement of the pungency of the chilli peppers.
Each variety of the chilli has its own Scoville heat unit marked as SHU. This is a mathematical function of marking the heat level of a particular chilli pepper by its capsaicin concentration. The chemical compound capsaicin is the active component that is present in the chilli sauce that is responsible for the heat sensation when it is tasted by humans.