The Comfortis chew contains a new flea-killing ingredient called Spinosad. Most flea-killing products acts within 24-48 hours, while this one will start terminating fleas within 30 minutes! In less than four hours, your dog will be completely free of any flea. Let your dog chew a Comfortis tables once a month, and you won’t know about the existence of these parasites. As Comfortis works from the inside, your dog may swim or bath as much as he likes. The product cannot be washed or rubbed off his skin. It is a great product for dogs with skin allergies.