I applied the Hartz flea and ticks drops for cats and kittens on my 1 year old cat Clementine. As soon as I put the drops her skin turned red and she started panting extremely quickly. She immediately ran under my bed, I got her out of there to wash it off with dawn soap and water. She was still breathing heavily for about 6 more hours and then she threw up. She is thankfully fine now but I consider myself lucky.