Roughly a year ago I gave my cat who was only a year old at the time a Hartz flea and tick collar. I noticed about 2 days later the skin was completely raw and bleeding. I thought maybe I had the collar on to tight (even though I did check to see If it was to tight when I put it on) I loosened it and kept it on for a few more days. Over the next few days I noticed her entire neck was raw, bloody, and she was acting weird. I took the collar off and applied neosporin for about two weeks, her neck healed up. Until I stumbled across this website today and I never thought it was the collar that did this to my baby, so Thank You for the warning. I’ll never use any of the products again.