6 reasons why it seems like your Seresto collar isn’t working

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The Seresto Flea and Tick Control collar is a popular choice for dog and cat owners trying to get rid of fleas and ticks on their pets. Sometimes it might seem as though your Seresto collar is not working as you might expect, but there may be a few reasons for this.

How does the Seresto Flea and Tick Control collar work?

The Seresto collar contains two active ingredients; imidacloprid and flumethrin. Imidacloprid is the active ingredient that kills the adult fleas and flea larvae in your pet’s immediate surroundings.

The collar’s innovative technology gradually releases controlled doses of the active ingredients over a long period of time. The ingredients are transferred to your pet’s skin and coat and spread across their entire body surface, keeping them protected from fleas and ticks for 7-8 months. Seresto is clinically proven to kill fleas within 24 hours and actively repel and kill ticks through contact, so no bite is required for it to work*.

Dog inside wearing a Seresto Flea and Tick Control collar

6 reasons why your Seresto collar may not appear to be working

Sometimes your Seresto collar may seem like it’s not working. Let’s look at some of the reasons why this might be.

1. You may own a fake Seresto collar

If your Seresto collar doesn’t seem to be effective against fleas or ticks, it may be a fake. Some popular online marketplaces offer Seresto collars at what might seem like good prices, but unfortunately these are often counterfeit. If it’s fake, the product is unlikely to contain the correct ingredients and you may not see the results you would expect.

You can be confident you have bought a genuine Seresto collar when you purchase from your vet or one of our official retailers.

If you’re concerned you have a counterfeit product or want to know how to spot fake product, read our guide.

2. ​Your pet has only just started wearing the Seresto collar

As the active ingredients are stored within the Seresto collar, when it is first applied, it is worthwhile noting that it can take 48 hours for the active ingredients to reach optimal levels to start fully affecting fleas and ticks.

However, if your pet has brought fleas into the home, it’s likely you will need to treat your home for an infestation as well as your pet. This is because by the time we notice fleas on our pets, it is often the case that the flea population is well established within our homes.

It’s believed that about five per cent of the flea population is found on our pet and the other 95 per cent is within the home environment at different life cycle stages: eggs, larvae, pupae and adult fleas.

Because of this life cycle, it can be normal to see fleas around the home for some time after treatment, as such, it may take weeks or months to get rid of a large flea infestation. However, once they jump onto a treated pet, they should be subsequently killed within 24 hours.

When tackling a flea infestation, it is important to use a veterinary recommended spray for your home. Read about the importance of breaking the flea life cycle and how you can rid your home of fleas.

3. Your pet already has ticks

As well as preventing fleas, Seresto is an effective tick treatment. If your dog has a tick attached to it before you put the collar on, it can take up to 48 hours for these to be killed so we would generally recommend removing any ticks that are already attached. If you’ve spotted a tick on your pet, use our guide to removing ticks.

However, once your pet has been wearing their collar for 48 hours, new ticks that jump onto your pet and try to attach will be actively repelled and killed.*

4. Other pets are re-infesting your home

You need to treat all of the pets in your house, not just the one that you’ve spotted the fleas on, otherwise pesky fleas will keep infesting your home and continue hopping onto your pet from the untreated ones.

Even if you don’t have any other pets, your dog can still pick up fleas if they meet dog pals at the park or kennels, and infested wildlife. To avoid this, try to keep your dog away from stray cats or wildlife in your garden, and if your pet is visiting a kennels or cattery, make sure you ask what their flea prevention strategy is. If they don’t have one, you might want to consider one that does.

Dog and cat on sofa being petted by owner

5. Your pet isn’t wearing their collar continuously

The collar works by releasing its active ingredients continuously in low doses onto your pet’s skin and coat. It is these active ingredients that kill fleas and ticks when they make contact with your pet’s skin and hair. If the collar is removed, it is not able to continuously release its active ingredients onto the skin and hair and your pet will not be protected.

To keep the collar working optimally, check and adjust it regularly so it’s fitted correctly around your pet’s neck. It should not be too tight or too loose – you should be able to comfortably fit two fingers between the collar and your pet’s neck. Watch our video to help you correctly put the collar on your pet.

Dog on sofa in the home

6. Your pet swims or is bathed a lot

The great news is that Seresto is water-resistant and remains effective if your dog becomes wet, so there is no need to remove the collar for swimming or having a bath. However, prolonged, intense exposure to water or extensive shampooing should be avoided as this can potentially reduce the duration of activity.

Studies have shown that monthly shampooing or water immersion does not significantly shorten Seresto’s 7-8 months of efficacy when it comes to ticks once the active substances have been redistributed across your pet’s coat. However, for fleas, Seresto’s efficacy gradually decreases starting from the fifth month.

If you have looked at the advice posted here and still feel that your Seresto collar is not performing as you might expect, please get in touch via the ‘Contact Us’ link below, alternatively you can contact your local vet practice.


*Mehlhorn et al. Parasitol Res (2001) 87:198-207, information is regarding mode of action and is not intended to relate to speed of kill or to imply parasites can be completely stopped from biting. An attachment of single ticks after treatment cannot be excluded; for this reason, a transmission of infectious diseases cannot be completely excluded if conditions are unfavourable.

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