Could this be harmful to me?

When I use my laptop, I actually have it on my lap... Lately it's been getting really warm and it leaves the top of my thighs red. I didn't think anything of it at first, but a few days ago I noticed a slight discoloration of my skin on my left thigh. It made this part of my skin a little darker..It's really only noticeable from close up. Could this be harmful to me?