What Causes Rashes On The Buttocks?

I work in a factory thats very hot and humid and I tend to sweat. I also wear boxers, I don't know if that has any thing todo with it. But I come home some times and I've for two rashes on the inside my butt cheeks on the walls, Kinda like chalfing Is there any way you know what this is or how I could prevent it? Or cure it?