Based on the pictures (it appears brown in color?)...if so then I have 2 thoughts.


1. Scale Rot - early stages. Usually a result of too moist of a substrate and/or high humidity. The constant dampness causes the scales to rot - it is bacterial so you will need meds.

2. A light burn - do you have any heat rocks, or a UTH that isn't on a thermostat, exposed light bulbs in the cage?

Either one means you need to get him to a vet to check him out.

Maybe someone else will have other ideas.