Ok, I'm pretty sure from reading your post that you scratched your rear AFTER you arranged the spices. Of course, you probably had some of the hot stuff from the peppers on your hand that got on your skin when you scratched; hence the burning sensation.
About the milk thing; I remember reading somewhere on a cooking forum that there is something in milk that absorbes the hot stuff from the pepper. Someone on that forum got pepper in her eyes and was told to wash it out with milk; worked for her