Kills and Repels Kills and repels fleas and ticks by contact so pests don’t have to bite your dog to die. Same-Day Effectiveness Starts to kill and repel fleas within 24 hours of initial application and kills reinfesting ticks in as few as six hours. Vet-Recommended #1 selling, non-prescription flea and tick brand stocked by 8,000 vet clinics.* *Elanco – Data on File How to use Step 1 Be sure to attach the collar tight enough to ensure the collar is always coming into contact with your dog’s skin and hair. Step 2 Use the 2-finger rule: insert the end of the collar through the buckle, then adjust the collar so that it is possible to hold two fingers comfortably between the collar and the neck. Step 3 Pull excess collar through the loop(s) and cut off extra collar, unless it is on a growing puppy.See package insert for details. Frequently Asked Questions How long does it take to work on fleas? Seresto kills existing fleas on dogs within 24 hours after application. After those 24 hours, new fleas are killed within 2 hours. How do I know if the Seresto collar I purchased is authentic? It is crucial that pet owners purchase real and genuine Seresto products from authorized and trusted retailers. Counterfeit collars and their packaging look very similar to the actual product. Be sure the collar does not have a greasy feel or an odor. Does it expire? There is no expiration date required on the packaging. The product should be kept in its original packaging and stored as directed on the label. What are the key ingredients? The active ingredients in Seresto collars are Imidacloprid and Flumethrin: Imidacloprid to help protect against fleas and Flumethrin to help protect against ticks. No other product has this combination of ingredients.