Instruct: Classify a given review as either positive or negative.
Query: It works, but PLEASE be careful!

I used this product on my cat for years--since his kittenhood, and he's now eight.I never had a problem until recently. It appears now when I use Frontline that he has an allergic reaction to it; a silver-dollar sized chemical burn appears within hours of application, and within a day he has a bald spot to accompany it.He is now enduring twice-daily hydrocortisone treatments and a sweater vest made from an old sock. (Have you ever tried to put a 16 lb cat in a sock? I caution you; it is an exercise in patience and dexterity.)