The Seresto cat collar kills fleas through simple contact, which means the fleas don’t have to bite your cat before they’re killed. Key Features: Kills fleas and ticks on cats and kittens of all weights and 10 weeks of age and older. Starts to repel and kill fleas within 24 hours of initial application and re infesting fleas within two hours Also repels and kills ticks within 48 hours of initial application and re-infesting ticks within in six hours Easy-to-use adjustable collar is odorless and non-greasy; quick-release feature and visibility reflectors provide extra safety. The water-resistant formula continues working for up to eight months, even after bathing and sun exposure.