Sounds like it might be a burn/ blister? Trip to the vet for sure any how. What type of heating source are you using ? What type of enclosure, temps , humidity do you have dialed in? Are you using a thermostat to regulate your heat sources?
Sounds like it might be a burn/ blister? Trip to the vet for sure any how. What type of heating source are you using ? What type of enclosure, temps , humidity do you have dialed in? Are you using a thermostat to regulate your heat sources?
^This^
Without having pictures and knowing a little more it's hard to provide any help.
If your heat source is unregulated please unplug it ASAP until you can purchase a dimmer switch as a temporary measure and order a thermostat.
Following this replace the substrate by clean paper towel.
IFThis is a burn depending on the extent it may require a trip to a vet.