Possible substitutes for red pepper flakes include cayenne pepper, Chile de Arbol, chile paste or a small red chile. Because all of these different types of chiles vary in heat from red pepper flakes, it is important to adjust the amount added to a recipe accordingly. For a recipe calling for 3/4 teaspoon of red pepper flakes, use 1/2 teaspoon of cayenne or Chile de Arbol as a substitute.
Chile paste is more mild than red pepper flakes, so the amount of red pepper flakes called for in a recipe can be doubled to obtain the same level of heat. One small red chile, such as a Thai chile, can also be used in place of 3/4 teaspoon of red pepper flakes. Thai chiles are considerably hot, so remove the peppers' seeds, which contribute greatly to the spice level of a pepper, before using them to decrease heat and more easily match the spice level of red pepper flakes.
Red pepper flakes are commonly made from cayenne peppers, making cayenne powder the best substitute in terms of flavor and heat. Red pepper flakes are also called crushed red pepper, crushed pepper flakes or pizza pepper. They are most often used as a condiment to add heat to a number of items, including pizza.