I thought flea collars were safe, until last night when my cat Sam wanted me to hold him. I turned him over on his back to rub his belly, and seen that around his collar had NO hair! If I had done my research before buying flea meds I would have stayed away from Hartz. Luckily the vet says that we took it off of him quickly enough, and we gave him a bath with Dawn dish soap. She said that he will be OK as long as he doesn’t start with the Diarrhea and Vomiting.