A couple weeks ago I put a Hartz tick and flea collar on my cat Spaz. Last night it fell off and this morning I noticed that my poor baby had lost all of his hair around his neck where the collar was and there was a white substance on it. It wasn’t bothering him but I gave him a bath and now that the residue is off it looks a lot better. I wish I had known about this site before I put one on my fur baby. My kids were so worried about our Spaz. I will never purchase another Hartz product again. From the looks of the previous posts we definitely got lucky this time.