I gave my 6 year old poxer Mickey a flea bath with Hartz shampoo and by the next day, he had almost chewed his tail through! I took him to the vet and he had a fever of 103! He was absolutely miserable, shaking, panting, randomly running through the house and chewing himself to death. The vet said it was either chemical burns or an allergic reaction. He gave prednisone and luckily my little guy has finally healed.