That's really wierd! I don't think your dog could bring anything into the house that would do this.
I'd suggest taking out all the plants/decor/substrate and putting him on only newspaper/ papertowels with a plastic hide (for easy cleaning) and just keep it as sterile in there as possible for the time being. Whipe the affected area with betadine/peroxide and then apply a triple antibiotic or neosporin w/o pain reliefe once or twice a day. Maybe see if that helps

Also, it wouldn't be a bad a idea to seek out another vet for a second opinion at this point. I
think you could even get a culture/biopsy done on his chin to see what exactly is affecting the scales.