BLUE TONGUE SKINKS

Today I came home to see that my adult Northern has a black spot on his chin. He definitely didn't have it last time I looked him over so it happened within the last day. It's definitely not mouth rot. The most likely cause seems to be a burn, but upon googling "reptile burns" it doesn't look like any of those burns. It looks like he rubbed away part of his chin scale and there was black/bluish/purplish underneath.

The black area is the same texture as his other scales (maybe very slightly rougher). It doesn't appear particularly painful or sensitive to the touch.

Just yesterday I moved him home to his temporary enclosure at my parents' house; I have an apartment at college, but I bring my herps with me when I go to my parents house which is only about an hour away. The two sources of heat are a 100 watt ceramic heat emitter (the main source of heat) and a mini undertank heater. Since moving him to his new tank he has been spending most of his time cuddled in the folded towel over the undertank heater. However he always crawls into the towel (not under the towel to lay directly on the hot glass) and even if he did lay against the hot glass I would think his belly would be burned not this one very specific spot on his chin.

He has been in this exact same setup before when I've been home for breaks and never had any issues. I have an infared temperature gun and I haven't been able to find any spot in the tank that gets over 95ish degrees. Northerns can have basking spots up to 100 degrees so I don't think a normal basking temperature spot would burn him. It's also strange that just the scale directly under his mouth on his chin seems to be effected.

He doesn't seem to be in any distress. Should I just keep him under observation and disinfect the spot with Betadine/Nolvasan? I've treated major shell rot in an aquatic turtle multiple times so I know how to keep reptile wounds clean (though this really doesn't seem like a wound either).

I'm just so mystified as to 1) what exactly this black spot is and 2) how the heck did he burn/injure himself?

I've tried getting a picture, but it's really difficult in the shadowy night lighting with a squirming skink. I'll try to post one in the morning.

Any chance he's stretching up to the CHE? Just a quick touch could easily burn.

I realized that when I brought him home and put him in the temporary enclosure for the first time I turned the heat in the room way up so it would get warm fast (the room was a bit on the cooler side). His temporary tank is right next to the baseboard heater so for the short period that the heat was turned up full blast (I turned it down once the room got up to temperature) it would have made the part of the glass near the heater super hot. My skink likes to rest his chin on the glass so that must have been how he burned himself.

Took him to the vet today. He gave me silver sulfadiazene to apply to his burn daily. My concern is that the burn is literally right underneath his mouth so when he flicks his tongue I worry that he is getting some of the silver sulfadiazine in his mouth. However I have noticed that silver sulfadiazene is recommended on the care sheet as a treatment for mouth rot so getting it in the mouth must not be too much of a concern if it's being used to treat lip/mouth infections? How worried should I be about him getting a little bit in his mouth?

Also do I need to just apply the ointment or does it need to be rubbed in? I don't want to hurt him by touching his burn.

While I was looking at his chin I noticed that the undersides of his top lip on both sides looked a little crusty and red, maybe like the very beginnings of mouth rot? From the outside his lips look totally normal, just that on top some of the scales are flared out a little bit instead of fitting snuggly against his mouth (not sure if that makes sense). I brought this up with the vet and he didn't think it looked like mouth rot. However he gave me some irrigation syringes just in case and said I could flush the area with 1/2 hydrogen peroxide 1/2 water. Should I do this or just leave it alone since the vet doesn't think it looks like anything to worry about? Or should I just cut back on wet, juicy foods for awhile (my skink has a habit of getting messy foods all over his chin/lip and then rubbing his face in the substrate and getting it all stuck to him, so that could have been what caused the potential infeciton in the first place).

Any advice would be helpful. Thanks!

Silver sulfadiazine is often prescribed for wounds around the mouth, so I wouldn't worry too much about him getting small amounts of it on his tounge. Just treat the wound as directed.

The scales on his upper lip that are slightly turned out are very normal. Unless they are starting to look inflamed, I would simply try my best to keep the areas clean and free from build-up. I've had several skinks with mouth-issues, and have found that brushing the lips with a soft baby-toothbrush can be helpful; softening any build-up with water first, then gently brushing the area.
I also have treated mouth-sores with a ophthalmic tripple-antibiotic ointment from my vet; if the areas start looking more red you could ask your vet about that.