Seresto Flea & Tick Collar DogSeresto Flea & Tick Collar The active ingredients in Seresto are specially formulated for steady dose adjusted release that spreads over your dog, remaining in the fatty layer of the skin and coat, where they are effective against fleas and ticks all season long. Fleas don't have to bite your dog to be affected, so your pet suffers less of those painful bites. It also effectively repels and kills ticks, preventing them from attaching to your dog. Key