Small red rash on small of back?

Earlier today after completing my regular regimen of sit-ups on my carpet floor with my shirt on I noticed a small red rash on my back. It does not hurt, it is not raised, the affected area is not scaly nor itchy. I was worried that it could be skin cancer although it resembles nothing like a skin cancer. Could this just be some sort of irritation caused by the carpet? I am clueless and quite worried.