Kills all existing fleas on your pet within 18 hours. Each application provides a full month of protection. Also aids in the control of sarcoptic mange infections. Great for pets that swim since it's waterproof. Kills ticks and chewing lice. It contains fipronil, a broad-spectrum insecticide and slow-acting poison that disrupts the central nervous system of fleas and ticks and S-methoprene, an insect growth regulator that kills flea eggs and larvae. The active ingredients are stored in the sebaceous glands and are wicked out of the hair follicles and continuously re-applied to the coat for long-lasting, waterproof protection.