I Have Been Using A Heating Pad On My Legs

I have been using a heating pad on my legs above the knee. My right leg was picking from a disc hitting the nerve in my right leg. i just had back surgery and they shaved the disc. but now I have red blotches all over both legs above my knees. I pretty much have had that heating pad on all the time. Is this what has caused the red blotches? and will it go away? Should I worry about this?