Seresto collars are designed to provide 8-months of flea and tick prevention, although in some cases they may last even longer than that. They typically remain effective for up to 8 months, as long as it is not exposed to water more than once a month. The active ingredients in the collar slowly release over this 8-month period, providing your pet with continuous protection so that you don’t have to worry about reapplying a flea and tick medicine every month. Additionally, Seresto collars repel other biting pests such as mosquitoes and sand flies.