I Have Red Blotches/rash On My Stomach That Come And

I have red blotches/rash on my stomach that come and go. It doesn't hurt or itch. It is not raised. It just shows up from time to time and stays for a week or two and then goes away. I don't have any food allergies that I am aware of and haven't change any soaps or detergents lately. I am 32 years old and am in good shape/health.