Need to see it, but do consider whether it might be a burn? Check cage for safety issues (-don't wait). Burns can be quite serious, & no matter what,
they're painful & slow to heal, & can impact everything your snake does (eating, shedding, & being able to be handled as a pet).
What kinds of heat are you using in his cage? Are they controlled by a thermostat? What are the temps. in the cage? (highest & lowest)