What are you using to heat the enclosure?
If you're using a heat pad, do you have it regulated with a lamp dimmer or thermostat?
What are you using to monitor temperatures? Probed or analog thermometers or a heat gun?

75 is too low and brings the chance of him getting a respiratory infection. Keep it no lower than 78!

It looks like a burn to me, I'd be taking him to the vet.