HELP REQUIRED

Can't get in contact with vets. What is this under my kittens chin

My first thought was feline acne but the area seems too big for that. I really think a vet visit is in order. Unless you can show the vet a picture before you get there, he or she probably wouldn't be able to do any kind of diagnosis without seeing the cat. If you are having trouble getting a hold of a vet, try your local humane society. Some of them have low cost vet clinics associated with them or can refer you to one. If you need help finding assistance, please let us know where you are located and we can help you find one. I think that it's better to be safe than sorry.

Welcome to TCS. I hope your cat is OK.

I have had cats that had this and am pretty sure it was flea infestation related. Could that be the case?

It could actually be chin acne that's gotten infected.  Do you use plastic bowls and dishes?  If so, switch to ceramic or stainless steel.  Get him to the vet to get a good diagnosis, too.