Yeah just consider your individual risk factor and go from there. I had just moved into a new apartment and I'd bought the carpet from the previous owners, who had a dog. I think maybe that's where the fleas came from - but I have no idea. Just shows how easily it spreads in the summer.The last flea infestation I had was because a foster cat was infested and I didn't realize until after I'd let her out all over the apartment. I didn't really dose either of them this summer since we didn't have fosters, and no infestation yet. But regardless, if I'm taking Mishka out, I think I will dose both of them just to be safe. It was too painful to deal with last time.