Capsaisin is the chemical in chili peppers that makes them spicy. It is fat soluble. This is important to know for two reasons:
1. When you eat something too spicy, chase it with cream cheese instead of water - fatty items will bind to the chemical and remove it from your taste buds.
2. When you want to make your food spicy, add the red pepper flakes into the hot oil at the initial stages of creating whatever it is you are creating. (You know how a lot of dishes start with sauteing garlic in hot oil first? Add the spicy stuff then.) This prevents you from eating a dish and saying, "You know, it's really not that spicy," before isolating a lone red pepper flake on your tongue that burns a hole through your taste buds.
Quick trick: Anyone who has been to Italy has seen the spicy olive oil served at restaurants. Italians often pour red pepper flakes into their olive oil and let it sit for a few days, allowing the olive oil to take on the heat. It's a great "ingredient" to incorporate in your cooking or to add on top of your finished meal.
Source: http://www.wisegeek.org/what-is-capsaicin.htm
