Hot peppers, also known as chili (or chile) peppers, owe most of their "heat" or pungency to a chemical substance called capsaicin. This chemical is concentrated in the cross walls of the fruit and around the developing seeds. Chili peppers can be mild to fiery hot, depending on the amount of capsaicin present. The amount of capsaicin in peppers is measured in Scoville Heat Units (SHU). Currently, the hottest pepper is considered to be the 'Carolina Reaper' which has 2.2 million SHUs. A combination of genetics and environment are responsible for the amount of heat in hot peppers. Peppers that do not contain capsaicin, such as bell peppers (0 SHUs), are considered "sweet." In addition to the hot types, other specialty peppers include sweet varieties of unusual shape, size and/or color.