I use advantage on my cats and my Sunny had a similar reaction. I freaked out and took him to the vet. My vet gave him a shot of cortisone to help stop itching and said to leave it alone. It healed up by itself in a few days. He said to put the advantage on different areas of his back each month. Storm also had this reaction but it wasn't as bad. Now I put the advantage on different areas of their backs each month and I haven't had a problem since. Good luck.