Rash or poisoning caused by flea collar?

Never us a flea collar on a dog or a cat. They are highly toxic. The best thing to do is to bathe your dog frequently. Keep their bedding clean. The best kind of flea treatment is the oral kind. It's natural and won't hurt your dog. Since your dog is having a reaction to the collar, maybe you could use a topical antibiotic to the affected area. There are also a lot of soothing dog shampoos. Good Luck and God Bless.