9 Reasons Your Flea Treatment Product Doesn’t Work

A flea infestation is annoying at the best of times, but if you have been using a flea treatment on your pet and you still suffer an infestation it’s doubly irritating.  Why is it that sometimes, despite our best efforts, our flea treatment lets us down?  Let’s look at a few of the top reasons why your flea treatment isn’t working. 

You Treated Your Pet, But Not Your Home

This has to be one of the most common causes of a flea treatment not working.  Many people think that if they use a spot-on treatment, for instance, the problem of fleas will be solved.  It won’t.  The spot-on treatment will address the fleas on you pet, but there will still be plenty of fleas living around your home.  Take care of them too, or these immature stages of the flea will soon mature and jump back on to your pet and start the cycle off all over again.
Even if you use a spot-on treatment with an IGR (insect growth regulator), you should keep hoovering daily if you have an active flea infestation.

You Used a Treatment that Only Kills Adult Fleas

This is related to the reason above.  There are many effective flea products on the market, but they only do half a job.  They kill adult fleas on your dog.  This includes most flea shampoos, flea collars and some oral treatments like Capstar.  These products are great for clearing your pet of the adult fleas already on his body, and if he suffers from flea allergy dermatitis, it’s a good thing to do.  Just make sure you follow it up with a treatment that targets the immature stages, like a spot-on treatment with an IGR .  Hoover regularly.

You Had a Break in the Treatment

Fighting fleas is an ongoing battle; you can’t take a holiday.  Fleas will sneak in, given the slightest opportunity.

 If you have a flea treatment that needs to be administered every four weeks, make sure you keep to the schedule.  If you prefer to use natural flea treatments, say garlic, use them regularly.  Comb your pet, or check flea traps, to keep one step ahead of a flea infestation.  Hoover several times a week and wash your pet’s bedding at a high temperature.
Sometimes vets suggest that you can take a break from treatments during the winter months.  This seems like a great idea, as fleas aren’t active during cold weather.  However, if you stop the treatment and the winter months turn out to be milder than usual, you could end up spending a lot of time, money and energy fighting a flea infestation.

You Didn’t Apply the Product Properly

I’ve nearly been caught out when using a new product before.  I assumed that all spot-on treatments would be administered in the same way – I now know that they are not!  Fortunately, I double-checked the instructions just before I applied the whole vial between my dog’s shoulder blades and found that this new product needed to be placed at three spots along her back.

The other thing that people sometimes do is just splash the product on top of their pet’s coat.  Make sure that you part the fur and get it on to the skin.  Remove a patch of fur if necessary.

You Didn’t Give the Correct Dose

This one caught out both myself and my vet.  My regular spot-on appeared to have become ineffective, despite a couple of years of successful use.  We decided to check my dog’s weight and the result was that we upped her dose and all was fine once again.  

You Don’t Understand How the Treatment Works

Flea products work in different ways, depending on which ingredients they use.  Some can have surprising effects.  For instance, the main ingredient in Frontline affects the fleas’ nervous systems, causing them to become more active and visible before they die.  Some pet owners witnessing this apparent explosion in the flea population think that something has gone wrong and the product doesn’t work.

Capstar on the other hand, and products like it, give a very quick result with adult fleas dying quickly.  However, in a few days, you may notice your pet re-infested as immature fleas are not affected by the treatment.

You Didn’t Empty Your Vacuum Cleaner Bag

It seems such a small thing, but if you do all the right things, but forget to empty your vacuum cleaner and dispose of the bag outside, fleas can mature inside the bag and hop out to re-infest your home.  Take a few minutes to get rid of the bag, or keep a flea collar inside it.

You Didn’t Treat Your Car

If your pet travels in your car, you need to treat the car too.  Deal with it just as you would your home, vacuum the carpet and dispose of the bag.

Your Treatment Has Become Ineffective

I’ve read a lot of anecdotal evidence, including some from vets, that in some part of the world, some flea treatments are not working.   The two most commonly mentioned are Stronghold and Frontline.  It should be noted that there are many more people using these products successfully.  However, if you feel that you apply the product correctly and treat your home effectively and you still have a flea problem, speak to your vet about changing to a different product.


  • Whichever flea treatment you use, you need to administer it regularly and according to instructions.
  • Treat your pet and your home.
  • Don’t forget to treat everywhere your pet goes, including your car.