Five reasons flea treatment for dogs might not work

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A common topic vets get asked about is how to get rid of fleas on dogs. “Why is my pet’s flea treatment not working? What’s the best way to get rid of fleas?” Often followed by: “I heard there’s a resistance issue with some flea treatment for dogs”.

If you’re finding fleas on your dog despite using a flea treatment, here’s some of the most common reasons before considering you’ve picked up a new strain of drug resistant super flea!

Medication choice:

There’s a bewildering array of products out there for getting rid of fleas; collars, flea spray, spot-on medications, shampoos, flea powder, even flea bombs! Which works? The short answer: ask your vet.

Prescription flea treatments tailored to your pet’s needs and circumstances are far more effective than many ‘over the counter’ products, many of which frankly don’t work.

Application error:

With spot on treatments, application of liquid to the skin is crucial. If most of the vial is squeezed on the coat rather than the skin by carefully parting the hair, then it won’t be as effective. Or only effective for a short period of time, leaving your pet prone to fleas before their next dose is due.

Wash off effect:

Have you washed your stinky hound after they’ve rolled in something pungent recently? Maybe they’ve had a dive in the river, or a dance in the rain? If you applied flea treatment just before, there’s a high chance it’s now been washed off before it can be fully absorbed.

Environmental flea burden:

Maybe you’ve suddenly noticed your dog scratching, and found fleas. But every day you’re finding more despite treating. Surely that must mean it’s not working? Actually, adult fleas on dogs are the tip of the flea iceberg. Chances are there’s hundreds more flea eggs and larvae in the environment, which continue hatching out weeks after an infestation is first noticed.

Using a suitable spot on or tablet from your vet AND treating the environment at the same time is the only reliable way to tackle a sudden or heavy infestation. Even with effective flea prevention for dogs, you might see dead or dying fleas for a while afterwards.


Most suspected cases of flea resistance can be explained by one or more of the above issues. If you’ve addressed all of those and are still battling a flea problem, speak with your vet about using a different product to help your specific set of circumstances.

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