Plastics and Rodent Ulcer

My Princess had a rodent ulcer on her chin from a flea collar. The collar was plastic. I took off the collar and watched the sore spot. It took about 4 weeks, but the hair grew back and she's good as ever!

I believe that "rodent ulcer" can be caused by irritation. Whether from plastic or something else, it looks like a rug burn would if we had fur.