What to do if I have painless red plates for months following prolonged exposure on an electric heating cushion used for a stomach ache?

Hello, It is possible that the lesions you describe are associated with erythema ab igne, a discoloration of the skin in response to repeated or prolonged contact with a heat source. This usually does not require medical attention, especially if no pain is associated with it. Unfortunately, there is not much to do except wait. The darker the lesions, the longer it will take for them to disappear. Some lesions may never disappear. It is important to limit skin exposure to direct heat. Consult a doctor if you see that the skin does not return to normal in a few months, or if you are very bothered by its appearance.