Low RiskMedium RiskPet Products

Flea prevention poisoning in cats

Flea prevention poisoning is one of the most common poisons in cats.   The topic of flea control is controversial and complicated. Since cats are especially sensitive to any treatment or medication, understanding how various treatments work is important.

Flea prevention poisoning in cats
We share our love and our fleas!

There are horror stories out there in regard to people who have applied some form of treatment to their cat and had awful adverse reactions.  The topic is so stressful, many people avoid treating their cats year-round, or avoid treating their indoor kitties altogether.   Since fleas can hitch a ride on your shoes and clothes (or your dog!) to infect your indoor cats, this often leads to household flea infestations. So how do you tell what’s true and what will cause flea prevention poisoning?

Methods of application

Commonly, there are several methods of applying flea treatment to your kitty (or dog):

  • Topical drops – This is the standard between-the-shoulderblades method for monthly prevention.
  • Shampoos – We use these to bathe the fleas off and kill them.
  • Dust – Typically made with an insect killer, they go on dry via brushing.
  • Sprays – The moist form of dust. These come in flea treatments to spray directly on the cat, and formulas to spray onto your furniture (knowing the difference between the two is important).
  • Dips – Somewhere between a shampoo and a spray.  You completely soak your animal, but then you do not rinse it off.
  • Collars – Localized flea control that contains prevention in the collar instead of directly on your cat.
  • Orally – Monthly preventatives in pill form.

The main differences between these are the methods of application.  In many cases, the active ingredients used in these products are the same.

Ingredients in flea prevention

Active ingredients

The active ingredients in any flea control product are the ingredients that work directly on the fleas.

Active ingredients
My active ingredients are fipronil and s-methoprene

The active ingredients of a flea product fall into two types:

  • Adulticides – This is a fancy name that just means it directly kills adult fleas.
    • Common adulticides:
      • Fipronil – Found in Frontline.  May cause some mild skin irritation if a cat is allergic or sensitive to fipronil, and may cause some mild tummy upset and drooling if swallowed.
      • Pyrethrum/Pyrethrins – Chrysanthemums naturally produce these chemicals. The adverse effects are similar to fipronil. However, these can cause more severe effects like tremors and seizures if your cat comes into contact with a highly concentrated form (such as a spray for the yard or a spray used on farms).
      • Pyrethroids – Lab-produced chemicals that mimic the pyrethrins created by chrysanthemums.  The ingredient that is extremely toxic to cats, permethrin, is a member of this category. Other pyrethroids (Like etofenprox) may cause a tingling sensation that can cause your cat’s fur to twitch and other odd behavioral changes in sensitive cats.
      • Imidacloprid – Found in Advantage.  The side effects are extremely similar to fipronil.
  • Insect Growth Regulators (IGRs) – Another fancy name that means the chemical prevents the fleas from being able to reproduce.
    • Common IGRs: Methoprene (Precor), fenoxycarb, and pyriproxyfen (Nylar)
      • All of these directly affect the fleas and have very little to no effect on your kitty.

Inactive ingredients

The inactive ingredients in these products are carriers that assist the flea-killing ingredient to absorb into the skin. These are the mild alcohols, oils, soap ingredients, water, dust particles, and anything else that’s not an insecticide.  These also include the scents and fragrances, if there are any. Inactive ingredients typically do not contribute to flea treatment poisoning in cats.  Again, if your cat is sensitive or swallows a flea-prevention liquid, it may cause some mild skin irritation or tummy upset.

Flea treatment poisoning

The following active ingredients are unsafe for use in cats:

Pyrethrin/Pyrethroids and Permethrin

Cats are sensitive to pyrethrins and pyrethroids, and permethrin is the most common ingredient to lead to flea treatment poisoning. Permethrin is a synthetically-produced form of pyrethrin.  It is a very common ingredient in flea and tick formulas for dogs.  Accidental permethrin poisoning in cats occurs when an owner applies a dog product on accident; when a cat lounges around on the dog’s bedding after treating the dog; or when a cat cuddles or grooms the family dog after treating the dog.

Sprays and bombs used for furniture/carpets and the outside yard frequently contain permethrin.  The simplest method of prevention is to check your labels. If you have a cat, avoid permethrin-containing chemicals completely. There are multiple types of flea prevention in dogs that do not contain permethrin.

Cats are sensitive to permethrins and may react to:

  1. Permethrin
  2. Cypermethrin
  3. Bifenthrin
  4. Other high-concentration pyrethrins/pyrethroids

The common signs of a cat exposed to permethrin are severe:

  • Constant drooling
  • Stumbling
  • Twitching
  • Muscle tremors
  • Dilate pupils
  • Seizures
  • Hyperthermia (an increase in body temperature from all of the muscle movement)
  • Death

An owner’s first instinct upon discovering that their kitty came into contact with permethrin is to bathe the product off.  Never bathe a cat exposed to permethrin without the explicit permission of your vet. While we do want the product removed, permethrin causes tremors and seizures.  The stress and rapid temperature changes that happen while bathing a cat can prematurely trigger seizures.

I’m hiding from my bath!

Unless your vet feels safe directing you to bathe at home, always head into a vet clinic and let your vet bathe your cat.  The stress of bathing can sometimes trigger a seizure, and your vet can reverse the effects right away.


Canine tick collars frequently contain the ingredient “amitraz”. Many owners believe that collars are generally safe, and take less care to check the labels than they would with flea drops. Again, cats who cuddle with or groom a dog wearing an amitraz collar can expose themselves.

Signs of amitraz poisoning in a cat are just as severe as the ones with permethrin poisoning:

  • Depression
  • Vomiting
  • Weakness
  • Stumbling
  • Unresponsiveness
  • Hypothermia ( a severe decrease in body temperature
  • Slow heart rate
  • Death

Like with permethrin, if you have a cat in the home, you should completely avoid using this product on your dogs.

3. Concentrated Essential Oils (The label will say 100% oil on it)

In response to the fear of causing a reaction in their cat, many owners have switched to trying natural solutions.  The problem is that some essential oils can be as toxic or even more so than flea products.  Kitties lack the appropriate enzymes in their livers to metabolize essential oils (and many other things).  This makes them extremely sensitive to natural remedies. Since essential oils are another large topic of their own, I won’t go into too much detail.  All essential oils are potentially toxic (tea tree oil being the most well-known), so avoid putting them on your cat completely unless they are formulated or recommended by a vet.

4. Using any product that is not labeled for use on cats

This one should go without saying, but we’ve all been in that place while looking at the price tag on a cat flea control product and wishing we could find a cheap generic.  The dog product or furniture/yard product you already have at home starts to look appealing.

But the products labeled for use in other creatures do not always mention feline safety.  Chemicals that are toxic to cats are not always toxic to other creatures, so they may contain ingredients that will cause flea prevention poisoning.  Paying the extra $15.00 will save you a lot more on vet bills later.

got fleas
One side effect of fleas is that your cat will eat their own feet.

But won’t flea prevention kill my cat?

A common complaint raised by nervous kitty owners is: “I read on the web that [insert any flea product name here] will kill my cat!” Let’s take a moment to delve into these claims and help ease your mind.

Topical drops are generally very safe for a few reasons:

  • The concentration of the active ingredients is very low – The dose needed to kill tiny fleas on a 10-pound kitty is not all that much. It’s much weaker than the dose that is needed to kill your cat, so the vial doesn’t contain enough chemicals to even be lethal. They’re mostly comprised of inactive ingredients.
  • The skin acts as a barrier to foreign chemicals – Your cat’s skin naturally prevents toxins from seeping into the body. While the carriers will help the chemicals reach the oil-secreting glands of the skin to help them in working properly, the amount that soaks into the bloodstream is so small as to be negligible.  Unlike essential oils, it’s just not going to reach your cat’s liver or kidneys.
  • Many products have been on the market for decades and are very well-tested – In the case of pyrethrins, we’ve been using them as pesticides for 100s of years (though not always on cats).  The side effects of these are extremely well documented. Even in the reported cases where cats have accidentally been given the topical drops in their mouths, they do not show life-threatening signs.

In the vast majority of cases where people report deaths in association with a particular flea treatment, the death of the cat can be traced down to one of two causes: another health issue that caused death around the time the owner applied the treatment, or the cat coming into contact with a dog that had used one of the toxic ingredients above.

Toxicity is directly related to dose.  The effects of any poison will depend solely on the amount of the poison that has been eaten/absorbed.  Flea drops like Frontline just don’t contain enough fipronil to cause flea prevention poisoning.

What are the common side-effects? 

Any application of any feline-approved flea treatment has the potential to cause the following:

  • Redness or irritation at the site of application (this can include loss of hair) – this is not a burn, as these chemicals are neither acidic nor alkaline.  These reactions occur in cats with sensitivities or allergies to active or inactive ingredients. Cats that show redness after the application of one product should switch to another.
  • Drooling – Cats groom, and they have extremely sensitive noses.  Foaming at the mouth after application is an extremely common (and harmless) reaction to the taste or smell of the flea treatment.  The drool will go away after flushing their mouth out with a tasty cat treat or some wet food.
  • Vomiting – This is also related to taste and smell.  If they lick a little off, or they really don’t like the smell, it might cause a cat to vomit.
  • Fur Twitching – The pyrethroid chemicals cause a tingling sensation in sensitive cats that has been likened to pins and needles.  The sensation is purely annoying and does not do damage to the cat. If a sensitive kitty is bothered by a tingly flea product, it can be bathed off with Dawn dish soap. Rubbing a drop of vitamin E oil on the application site can also ease the tingling.
  • Behavior changes like rolling, rubbing, crying, and hiding – This is also related to the tingling sensation, and is treated the same way as above.
flea treatment poisoning in cats
I’m hiding! They’ll never find me.

Flea prevention is actually healthy for your cat

Fleas can cause a lot of health problems in cats including flea bite allergies, tapeworms, anemia, and bartonellosis. Fleas can come indoors on your pants, on your socks, and simply by bounding through the door. So flea prevention is needed even for indoor cats!

As discussed above, with the exception of toxic ingredients, topical flea treatments are actually very safe for your cat and will NOT lead to flea prevention poisoning. If you’re still frightened about using a chemical on your kitty, talk to your vet about oral medications as an alternative.  Working with your veterinarian is the safest course of action you can take when trying to get rid of fleas. Before choosing a treatment, have them check your labels for you and verify everything there is safe to use in a home with cats.

One thought on “Flea prevention poisoning in cats

  • This is REALLY useful information…glad to have found it! Keep up the excellent work.


Leave a Reply