I can use for the outside cats since we can't touch them and if we could I wouldn't want to risk them licking off a spot-on product. My biggest worry with them is they will get fleas and we will carry them. My two senior cats do not use flea products (one has renal failure) and we only use natural products on Hooch due to his allergies...I don't kid myself. I don't think the natural ones are as effective, but since he hates grass and is rarely outside we've been fine so far.