Red pepper flakes are made from a mix of peppers from the capsicum annum family. Red pepper flakes, also known as crushed red pepper, are made from crushing dried chilies. The most commonly used pepper for crushed red pepper flakes is the cayenne pepper. The majority of red pepper flakes will be a mix of peppers, with cayenne taking up the majority of the share. The use of crushed red pepper on pizza goes back to the old country where it is a southern Italian favorite. It is great for adding a little heat to pizza and other traditional Italian foods. But with just a shake or two, it can add a little spice to otherwise boring soups, sandwiches, and salads. Crushed red pepper flakes will have a heat somewhere in the 30,000 to 50,000 Scoville heat unit range. This spice should be a staple in every home and spice cupboard, it can be added onto almost anything to give the dish a nice spicy kick!