Add red pepper flakes to the oil at the beginning of a dish so that it infuses throughout, but be careful because red pepper flakes become bitter when they burn. They are often a component in many Italian dishes and sauces, such as arrabbiata and aglio e olio, but you can also sprinkle them right out of the can onto pizzas, sandwiches, sautéed vegetables -- anywhere you want to add extra oomph.
Cayenne pepper adds discreet heat
Cayenne pepper is the dried and ground powder of cayenne chilies, named after the city of Cayenne in French Guiana. They are extremely hot, ranging from 30,000-50,000 Scoville units. But take note, because the store-bought spice you're about to purchase comes already ground, it will lose potency faster than whole chili peppers or even flakes.
Because cayenne is finely ground, unlike red pepper flakes, it's perfect for meat rubs, various marinades, and any dish that might need a more blended heat. Its flavor is fairly neutral and just adds a nice kick. Cayenne is also said to have many health benefits. Remember Beyonce's famous lemon-cayenne cleanse?