The condiment is made from hot dried red peppers and is not made of one type of chili, but from various combinations of ancho, bell, cayenne and other dried red peppers.
Crushed red pepper shakers have become as standard as salt and pepper on tables at Italian style restaurants and especially pizza parlors in the United States. Often there is a high ratio of seeds, which some people believe intensifies the heat of this flavorful condiment, whereas the heat actually comes from the vein of the pepper (pith) (off of which the seeds grow). Crushed red pepper is used in pickling, chowders, spaghetti sauce, pizza sauce, soups and sausage.
As chilis have become more popular, the varieties of peppers used to make crushed red pepper have also changed.