What Chemical Ingredients Are in Flea Treatments? - Cat Info Detective

What Chemical Ingredients Are in Flea Treatments?

Skye Blake looking left through magnifying glass

Skye Blake reporting in…

Here’s the scoop on the chemicals you’ll find as active ingredients in flea treatments. The more you know, the more comfortable you’ll be when choosing flea treatments for your favorite cat.

paw prints coming in from a distance

Don’t forget, the best way to keep you and your cat safe is KNOW WHAT YOU’RE USING and KNOW YOUR CAT!

The chemical ingredients listed below are various forms of insecticides. Your goal is to find what kills fleas best without hurting your kitty buddy.

kitten playing with a toy

I have not yet been able to dig up any studies about how cats are affected by these flea products over a lifetime use. If you have concerns, check with your veterinarian.

Both “chemical” and “natural” flea treatment products vary in:

  • ingredients
  • effectiveness
  • length of protection
  • control of other pests (lice, ticks, worms)
  • price
  • safety
  • ease of use
drawing of lab test equipment

Chemical Ingredients

(in alphabetical order)

When you read the chemical information below, you’ll see cautions about toxicity with various ingredients. Most are skin and other irritations caused by either too much being used (overdose) or improper application of the product (getting into mouth, eyes, nose, etc.). There are, however, a few notable exceptions that are very dangerous to us fabulous felines!


cat lying on his back

Bifenthrin (Pyrethroid Family): A broad-spectrum insecticide that interferes with an insect’s nervous system. It’s a chemical used for many different types of insects.

Bifenthrin can cause reactions in animals and people if touched, eaten or inhaled. These possible reactions could include vomiting, diarrhea, lethargy, twitching, drooling, hyperactivity followed by incoordination.

Cats, in particular, cannot handle being around Bifenthrin. Don’t use it in anything in a house with cats! 1http://npic.orst.edu/factsheets/bifgen.html2http://pmep.cce.cornell.edu/profiles/extoxnet/24d-captan/bifenthrin-ext.html3https://www.peststrategies.com/pest-guides/chemicals/bifenthrin/


Science Beakers with chemical liquid

Cyhalothrin (Pyrethroid Family): There’s also Lambda-cyhalothrin and Gamma-cyhalothrin. Gamma is a refined form of Lambda. It’s a more efficient chemical ingredient than either Cyhalothrin or Lambda-cyhalothrin. It disrupts the nervous system of insects.

Lambda-cyhalothrin is a restricted chemical pesticide and can only be bought and used by certified professionals. It’s commonly mixed as an ingredient with other pesticides. It’s toxic if swallowed and can cause convulsions and coma. Cats are especially susceptible. 4https://en.wikipedia.org/wiki/Cyhalothrin5https://pubchem.ncbi.nlm.nih.gov/compound/cyhalothrin#section=Mechanism-of-Action6 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/cyhalothrin7https://www.poison.news/2017-11-30-lambda-cyhalothrin-toxicity-side-effects-diseases-and-environmental-impacts.html 8https://ucanr.edu/sites/edc_master_gardeners/files/138969.pdf9https://www.petmd.com/cat/conditions/neurological/c_ct_organophosphate_carbamate_toxicity10https://vcahospitals.com/know-your-pet/pyrethrinpyrethroid-poisoning-in-cats


shaker of salt - DSS as a chemical ingredient of flea spray

Di-n-propyl Isocinchomeronate (MGK Repellent 326): A chemical ingredient in insecticides that’s always mixed with other insect repellents to make them more effective at repelling flea. It’s used on cats topically but is not to be used on cuts or open wounds.11https://archive.epa.gov/pesticides/reregistration/web/pdf/mgk_326_red.pdf 12https://oehha.ca.gov/proposition-65/chemicals/di-n-propyl-isocinchomeronate-mgk-repellent-32613https://pubchem.ncbi.nlm.nih.gov/compound/Dipropyl-isocinchomeronate#section=Overview14https://archive.epa.gov/pesticides/reregistration/web/pdf/mgk_326_red.pdf

Dioctyl Sodium Sulfosuccinate: Goes by many different names. Since DSS is a form of the chemical “sodium” (salt), it pulls water out of critters, which helps kill them. “It is used to kill and control not only fleas but also mites, ticks, lice and other pests. It works by affecting the waxy out covering of a flea’s physical makeup, slowly softening it. Eventually, the internal organs of the pest are also affected leading to the death of the insect.”15https://www.dogsbynina.com/best-flea-killing-shampoos-for-dogs

DSS is also used for constipation in humans (“Colace”), and animals.16https://www.drugs.com/vet/docusate-solution.html It has many other uses as a chemical ingredient in deodorants, air fresheners, etc.17National Center for Biotechnology Information. PubChem Database. Docusate sodium, CID=23673837, https://pubchem.ncbi.nlm.nih.gov/compound/Docusate-sodium18https://en.wikipedia.org/wiki/Docusate19https://www.cdhfinechemical.com/images/product/msds/31_348998187_DioctylSodiumSulphosuccinate-CASNO-577-11-7-MSDS.pdf


Test tubes for studying chemicals

Esfenvalerate (Pyrethroid Family): It quickly kills insects and is used in broad spectrum insecticide concentrates. Esfenvalerate is popular because of its low toxicity to people and is safe around pets when used as directed.20https://pubchem.ncbi.nlm.nih.gov/compound/esfenvalerate#section=General-Manufacturing-Information21http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/esfenvalerate-ext.html22https://en.wikipedia.org/wiki/Esfenvalerate

Etofenprox (Pyrethroid Family): A pyrethroid ether pesticide (rather than pyrethroid ester).  Disrupts the membrane of nerve cells.  Low concentrations make insects hyperactive.  High concentrations paralyze and kill them.

“Etofenprox seems to be less toxic for cats than other synthetic pyrethroids.  BUT:  cats are more suseptible to synthetic pyrethroids than dogs and do not support doses that are harmless for dogs.” 23https://parasitipedia.net/index.php?option=com_content&view=article&id=2682&Itemid=3044 Cats lack the liver enzyme glucuronidase.  This keeps them from breaking down synthetic pyrethroids, which remain in their body much longer than dogs and other mammals.24https://parasitipedia.net/index.php?option=com_content&view=article&id=2679&Itemid=304325https://parasitipedia.net/index.php?option=com_content&view=article&id=2786&Itemid=310726https://en.wikipedia.org/wiki/Etofenprox27 http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC3323128 http://www.fao.org/fileadmin/templates/agphome/documents/Pests_Pesticides/JMPR/Evaluation93/efenpox.pdf29https://pubchem.ncbi.nlm.nih.gov/compound/Etofenprox#section=GC-MS30http://veterinarymedicine.dvm360.com/toxicology-brief-10-most-common-toxicoses-cats


Scientist pouring chemical liquid into a test tube

Fipronil (Phenylpyrazole Family): Used for a wide variety of pests (ants, beetles, cockroaches, fleas, ticks, etc.)  It kills insects when they eat or touch it by affecting their central nervous system. Fipronil is more toxic to insects than mammals, since it’s more likely to bind to their nerve endings.

Fipronil can cause some skin irritation in people or pets.  If eaten, it can cause sweating, nausea, vomiting, headache, stomach pain, dizziness, weakness and seizures.31http://npic.orst.edu/factsheets/fipronil.html32https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf

Flumethrin (& Imidacloprid) in cat collars (Seresto® brand):  Effective for about 8 months.  Some cats won’t tolerate collars and might scratch the area, thus opening a wound where the chemicals can enter the bloodstream.  This might cause a reaction but there’s no evidence of side effects with normal use. 33https://www.ncbi.nlm.nih.gov/pmc/articles/PMC335315534https://www.epa.gov/sites/production/files/2017-01/documents/weighing_risks_to_children_from_dogs_wearing_seresto-tm_collars.pdf35https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/flumethrin

March 3, 2021: An article was published in USA Today claiming there’s an alarming number of deaths and injuries to dogs and cats caused by Seresto® flea collars. Is it legitimate or alarmist? See “Cat Flea Collars” for more about this claim.

cat scratching a branch

Fluralaner:  (Bravecto) On cats, it’s given topically between the shoulder blades and down the back so it can’t be licked off.  It’s distributed throughout the body and enters the flea or tick when they bite the cat, then die within hours.  Fluralaner kills only adult fleas and only after they bite the host animal.36https://vcahospitals.com/know-your-pet/fluralaner

Fluralaner is effective for 12 weeks in cats over 6 months of age.

Cats:  “The most commonly reported adverse reactions include vomiting, itching, diarrhea, hair loss, decreased appetite, lethargy, and scabs/ulcerated lesions. BRAVECTO is not effective against American dog ticks beyond 8 weeks of dosing. For topical use only. Avoid oral ingestion. The safety of BRAVECTO has not been established in breeding, pregnant and lactating cats. Neurologic adverse reactions have been reported in cats receiving isoxazoline class drugs, even in cats without a history of neurologic disorders. Use with caution in cats with a history of neurologic disorders.”37https://us.bravecto.com/for-cats38https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-016-1618-y39https://www.fda.gov/animal-veterinary/cvm-updates/animal-drug-safety-communication-fda-alerts-pet-owners-and-veterinarians-about-potential-neurologic


Scientist holding test tube

Imidacloprid (Neonicotinoid Class): Neonicotinoids are synthetic insecticides similar to nicotine but safer and more effective against insects.40https://fleascience.com/flea-control/

Imidacloprid disrupts the ability of nerves to send a normal signal so the whole nervous system stops working properly. It is much more toxic to insects than mammals and birds because it binds better to the receptors of insects.

In humans and pets, Imidacloprid doesn’t absorb well through the skin but can cause some irritation.  If breathed or swallowed, it can cause dizziness, breathlessness, confusion, vomiting in people.  If swallowed by pets, it can cause vomiting, drooling, trouble walking, tremors, tiredness.41http://npic.orst.edu/factsheets/imidagen.html42 http://npic.orst.edu/factsheets/archive/imidacloprid.html43 http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfop-methylparathion/imidacloprid-ext.html43https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf44 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/imidacloprid

March 3, 2021: An article was published in USA Today claiming there’s an alarming number of deaths and injuries to dogs and cats caused by Seresto® flea collars. Is it legitimate or alarmist? See “Cat Flea Collars” for more about this claim.

Indoxacarb:  An oxadiazine pesticide that kills flea larvae (among others) by blocking neuronal sodium channels.  It must be used carefully since some insects become resistant when exposed.45https://en.wikipedia.org/wiki/Indoxacarb46 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/indoxacarb47https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-067710_30-Oct-10.pdf48https://www.ncbi.nlm.nih.gov/pmc/articles/PMC273832149 https://www.domyown.com/indoxacarb-a-286.html50https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf


Lab beakers used to test chemical ingredients in flea products

Lotilaner: A newer isoxazoline used in chewable tablet form that can be fed to cats with or after their food. It’s claimed these tablets have a vanilla-yeast flavor that cats like, so it’s a no-stress way to give an oral medication. Data shows that lotilaner™ (by Elanco™) is highly effective against both fleas and ticks.51https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6043969/52 https://www.vetsurgeon.org/news/b/veterinary-news/archive/2018/11/13/elanco-launches-credelio-oral-flea-and-tick-control-for-cats.aspx

Methoprene (Insect Growth Regulator): It comes in 2 different forms – S-Methoprene and R-Methoprene

S-Methoprene works by acting like an important hormone in insects and interferes with insect growth and development.  It’s used frequently since it affects insects that survive exposure to other pesticides.

Methoprene can cause mild irritation in skin, eyes and lungs.  “In one study with very high doses (10 g/kg), dogs… showed signs like vomiting, dilated pupils, changes in behavior, breathing, and body movements.  When researches cut the dose in half (5 g/kg), the dogs had no observable signs or symptoms.”53http://npic.orst.edu/factsheets/methogen.html54 http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfop-methylparathion/methoprene-ext.html55https://www.centrallifesciences.com/active-ingredients/s-methoprene56 https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/fs_PC-105401_1-Jun-01.pdf

Keep in mind that cats cannot tolerate many things that dogs can, even in smaller doses.

Tabby cat paws crossed

Moxidectin:  an anthelmintic drug used to kill or expel parasitic worms from the host body.  It’s used in dogs, cats, horses, cattle and sheep.  

Moxidectin kills many parasites by binding to certain nerve and muscle cells.  This disrupts neurotransmission which paralyzes and kills the parasite. Anthelmintic drugs get rid of the worms without hurting the animal.

Moxidectin is sometimes used as an ingredient in combination with other flea and tick pesticides. Must be used very carefully in dogs and cats since it can be deadly if used incorrectly. Most of the information I found was for dogs. Moxidectin is also used in products for humans. 57https://en.wikipedia.org/wiki/Moxidectin58 https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/210867lbl.pdf59https://www.fda.gov/animal-veterinary/cvm-updates/fda-approves-proheart-12-moxidectin-prevention-heartworm-disease-dogs

“Do not use in sick, debilitated, or underweight cats.”60https://vcahospitals.com/know-your-pet/moxidectin-topical


Scientist testing chemical ingredients of flea products

Nitenpyram (Capstar) (Neonicotinoid Class): It is an oral flea treatment that absorbs into the blood of the host and gets into the fleas when they bite.  It works quickly to kill adult cat fleas and is effective for about 72 hours. Neonicotinoids are neurotoxins that act similarly to nicotine. They block neural signals in the central nervous systems of insects.

Nitenpyram is considered safe for humans but should still be handled carefully and not ingested.61https://www.ncbi.nlm.nih.gov/pubmed/14596282 62https://en.wikipedia.org/wiki/Nitenpyram

N-octyl bicycloheptene dicarboximide (MGK-264) (Synergist): A man-made chemical that works with pesticides to increase their ability to kill insects.  Synergists are not pesticides themselves.  MGK-264 is often mixed with pyrethrins or pyrethroid insecticides.

cat looking at cat tree toy

MGK-264 has the ability to stop some of the insect’s enzymes from working, thus giving the pesticide more time to work without being resisted.

It’s considered low to very low toxicity with no skin irritation.  Some eye irritation occurred in rabbits exposed to it. As with other products, adverse reactions depend on the dosage:  the higher the dose, the more likely a reaction will occur.63http://npic.orst.edu/factsheets/mgk264gen.html64 http://npic.orst.edu/ingred/mgk264.html65 https://www.restek.com/compound/view/113-48-4/MGK%20264(b)

Dose toxicity studies show a “high margin of safety in dogs and cats”66https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/nitenpyram67 https://academic.oup.com/jme/article/40/5/678/86407568 https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf


Microscope over a slide

Permethrin (Pyrethroid Family): A pyrethroid insecticide used for many things, including flea products for dogs.  It’s the most widely used mosquito killer in the U.S., because of “its low cost, high effectiveness, low incidence of pest resistance, and broad labeling”.69https://www.epa.gov/mosquitocontrol/permethrin-resmethrin-d-phenothrin-sumithrinr-synthetic-pyrethroids-mosquito-control

“Health effects from permethrin will depend on how someone is exposed to it. Dogs and cats that have permethrin on their skin may act strangely, and flick their paws, twitch their skin or ears, or roll on the ground. Animals that have licked treated skin may drool a lot or smack their lips. Cats that have been exposed by accident to products with high (45-65%) levels of permethrin may seem anxious and can’t walk normally. They may also have muscle tremors and seizures and they may die from the exposure.70http://npic.orst.edu/factsheets/PermGen.html71 https://en.wikipedia.org/wiki/Permethrin72https://pubchem.ncbi.nlm.nih.gov/compound/Permethrin#section=Preventive-Measures73 http://pmep.cce.cornell.edu/profiles/extoxnet/metiram-propoxur/permethrin-ext.html74https://www.epa.gov/mosquitocontrol/permethrin-resmethrin-d-phenothrin-sumithrinr-synthetic-pyrethroids-mosquito-control75https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf

Phenothrin (Pyrethroid Family):  (Sumithrin, D-phenothrin) A pyrethroid that kills adult fleas and ticks by disrupting their nervous system. It’s also used to kill head lice on humans.

Phenothrin is often combined with Methoprene. Some studies in Europe have shown widespread resistance to Phenothrin.

kitten looking out window

Phenothrin is no longer used in cat products as it has been linked to hair loss, salivation, tremors, seizures, and death in cats and kittens.76https://en.wikipedia.org/wiki/Phenothrin 77http://npic.orst.edu/factsheets/dphengen.html78 https://www.epa.gov/mosquitocontrol/permethrin-resmethrin-d-phenothrin-sumithrinr-synthetic-pyrethroids-mosquito-control79 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phenothrin

Piperonyl Butoxide (PBO) (Synergist – Insect Growth Regulator):  An organic compound that helps pesticides be more effective at killing bugs.  It’s often combined with pyrethrins or pyrethroids.  PBO stops some enzymes in the flea and gives the pesticides time to work.

It’s considered “low to very low toxicity if eaten, inhaled, or touched.  PBO is slightly irritating if it gets in the eyes or on skin.  It does not produce skin allergies.”80http://npic.orst.edu/factsheets/pbogen.pdf81 http://npic.orst.edu/ingred/pbo.html82https://www.beyondpesticides.org/assets/media/documents/pesticides/factsheets/Piperonyl%20Butoxide.pdf83https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/piperonyl-butoxide84https://www.drugbank.ca/drugs/DB0935085 https://medlineplus.gov/druginfo/meds/a601105.html


Lab tech looking through microscope

Prallethrin:  This pyrethroid insecticide controls mosquitoes, ants, fleas, etc.  It’s an effective ingredient against fleas and isn’t very toxic to humans, however, it can cause skin and eye irritation and other problems at higher dosages or greater exposure.86https://www.who.int/whopes/quality/prallethrin_spec_eval_Nov_2004.pdf87https://www.federalregister.gov/documents/2014/10/29/2014-25732/prallethrin-pesticide-tolerances88https://www3.epa.gov/pesticides/chem_search/hhbp/R086823.pdf89https://en.wikipedia.org/wiki/Prallethrin

Pyrethrins:  A mixture of six chemicals found in some chrysanthemum flowers that are naturally toxic to insects.  They help control mosquitoes, fleas, flies, moths, ants, etc. Chrysanthemum cinerariifolium is currently the flower used to extract pyrethrins.  

Pyrethrum powder is whole crushed mum flowers.  Pyrethrins are usually separated from the flowers.  Synthetic pyrethrins (pyrethroids) have been developed to make the chemicals longer lasting and more effective, thus better ingredients.  Pyrethrins are usually mixed with synergists (e.g, MGK-264) to increase their effectiveness.

Chrysanthemum cinerariifolium used to make pyrethrins, an active ingredient in some insecticides

Pyrethrins damage the nervous system of insects that touch or eat it, quickly paralyzing and killing them.  They’re low in toxicity to people and other mammals but can be irritating on the skin.

Pyrethrins are a popular insecticide for organic gardeners.90http://npic.orst.edu/factsheets/pyrethrins.pdf90http://npic.orst.edu/ingred/pyrethrins.html91 http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrins-ziram/pyrethrins-ext.html92https://en.wikipedia.org/wiki/Pyrethrin 93https:www.atsdr.cdc.gov/phs/phs.asp?id=785&tid=15394 https://www.saferbrand.com/articles/what-is-pyrethrin-is-it-safe95 https://www.epa.gov/ingredients-used-pesticide-products/pyrethrins-and-pyrethroids96https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf

You can make your own pyrethrin pesticide from daisies (Chrysanthemum cinerariifolium).  Be careful when attempting any homemade products. 97https://www.thespruce.com/pyrethrin-insecticide-definition-1902891[/mfn]


Test tubes
Pyrethroid Family of Insecticides (similar to pyrethrins but synthetic): It’s important to note that resistance to pyrethroids by insects is becoming widespread.

“Not all pesticides in the same class are equally toxic, or equally effective the same pests.  Nevertheless, most pyrethroid insecticides share the following characteristics:

  • Low in toxicity to mammals and birds;
  • High in toxicity to fish if applied directly to water;
  • Require very low doses to kill insects (high arthropod toxicity);
  • Fast-acting;
  • Especially effective against chewing insects, though many pyrethroid insecticides can be absorbed by the insect pest when it merely walks over the dry residue;
  • Bind tightly to soil and organic matter (therefore not as effective in penetrating soil to kill underground pests);
  • Dissolve very poorly in water.
Pyrethroids became popular as consumer insecticides in the 1990s as replacements for older pesticides, like diazinon and Dursban® that were phased out for environmental and human health reasons.  Some pyrethroid insecticides last a long time in the environment (days or weeks), especially when protected from sunlight.  Others, such as allethrin and resmethrin, break down within a few minutes to a few hours after application.”97https://citybugs.tamu.edu/factsheets/ipm/98 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC48087999 https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf


Scientist holding a beaker of red liquid

Pyridine: an organic compound with the chemical formula C5H5N. It’s a solvent and is used as a bulding block ingredient for many other products, including insecticides. Some products made from it have antiviral, anticancer, antimicrobial, antidiabetic, and antitubercular properties.100https://www.sciencedirect.com/topics/chemistry/pyridine

Too much pyridine is toxic and can cause dizziness, nausea, headaches, anorexia.101https://www.newworldencyclopedia.org/entry/Pyridine102https://study.com/academy/lesson/pyridine-structure-formula-physical-properties.html

Pyriproxyfen (Nylar):  (Synergist-Insect Growth Regulator) An ingredient that inhibits “the hatching of flea eggs and the development of flea larvae.”  It doesn’t kill the adult flea or any stages of ticks.

Pyriproxyfen is considered low toxicity to humans and mammals.  It doesn’t bother skin but can cause mild irritation if it gets in the eyes.  Moderate to large amounts can cause problems.103http://npic.orst.edu/factsheets/pyriprogen.html104 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/pyriproxyfen105 https://www.petcoach.co/article/pyriproxyfen-nylar


Lab beakers for testing chemical ingredients in flea products

Resmethrin (Pyrethroid family):  It was taken off the market December 31, 2015.  It’s an insecticide ingredient that controls mosquitos, midges and blackflies. Resmethrin is a chemical highly toxic to fish.106http://npic.orst.edu/factsheets/ResGen.html107 http://npic.orst.edu/ingred/resmethrin.html108http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrins-ziram/resmethrin-ext.html109https://en.wikipedia.org/wiki/Resmethrin110 https:www.epa.gov/mosquitocontrol/permethrin-resmethrin-d-phenothrin-sumithrinr-synthetic-pyrethroids-mosquito-control


Scientific equipment

Sarolaner (isoxazoline class): A chemical used as an ingredient in topically applied flea treatments for cats.  It’s never used orally. It kills fleas and other insects by affecting the nervous system.111https://www.ncbi.nlm.nih.gov/pubmed/28395750 112https://www.ncbi.nlm.nih.gov/pubmed/30579753113 https://www.fda.gov/animal-veterinary/cvm-updates/animal-drug-safety-communication-fda-alerts-pet-owners-and-veterinarians-about-potential-neurologic114 https://www.sciencedirect.com/science/article/pii/S0304401718303765115https://www.drugs.com/vet/simparica-sarolaner-chewables.html

Selamectin (Revolution®, Stronghold):  Topical parasiticide and anthelmintic (dewormer) for dogs and cats.  In cats it “prevents heartworms, fleas, ear mites, hookworms, and roundworms”. 116https://en.wikipedia.org/wiki/Selamectin117https://www.fda.gov/animal-veterinary/cvm-updates/animal-drug-safety-communication-fda-alerts-pet-owners-and-veterinarians-about-potential-neurologic

Selamectin kills fleas when they bite and suck the animal’s blood. It’s considered very safe for cats and dogs, with less than 1% having side effects.  These usually consist of temporary irritation or loss of hair at the application site.  Other symptoms would be from high volume of dying worms or other parasites in the animal’s body, not the selamectin itself.118https://en.wikipedia.org/wiki/Selamectin

Don’t use in sick, debilitated or underweight animals, or kittens under six weeks. 119https://www.zoetisus.com/_locale-assets/mcm-portal-assets/products/pdf/revolution-prescribing-information.pdf120https://www.ncbi.nlm.nih.gov/pubmed/10940537121 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/selamectin122 https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-018-2995-1123 https://www.researchgate.net/publication/12379291_Safety_of_selamectin_in_cats124https://www.ncbi.nlm.nih.gov/pubmed/28395750125https://www.ncbi.nlm.nih.gov/pubmed/30579753

tabby cat looking at camera

Spinetoram (Spinosyn Class): Spinosyns act completely differently than any other known chemical insecticide ingredients. “Spinetoram was more effective against fleas than fipronil/(S)-methoprene on cats. Spinetoram treatment significantly reduced signs of flea allergy dermatitis in cats…[and] resulted in a low adverse incident rate in cats.”126https://www.sciencedirect.com/science/article/pii/S0304401718302115127https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_G-4674_01-Oct-09.pdf128 https://www.plantmanagementnetwork.org/pub/php/perspective/2008/spinetoram129https://www.sumitomo-chem.co.jp/english/rd/report/files/docs/2012E_1.pdf

Spinosad:  A selective, broad-spectrum insecticide. “Spinosad is a natural substance made by a soil bacterium that can be toxic to insects… a mixture of two chemicals called spinosyn A and spinosyn D.”  It kills insects that eat or touch it by damaging their stomach and nervous system.130http://npic.orst.edu/factsheets/spinosadgen.html

Spinosad is not very toxic to people and other mammals.  It can cause some irritation and redness if it gets on skin or in eyes.  It’s used in organic gardening quite often.131https://aggie-horticulture.tamu.edu/newsletters/hortupdate/hortupdate_archives/2004/mar04/Spinosad.html132http://ipm.uconn.edu/documents/raw2/Spinosad/Spinosad.php?aid=9133https://www.ncbi.nlm.nih.gov/pubmed/15366583134https://ipmworld.umn.edu/thompson-spinosad135 https://webinars.veteducation.com.au/wp-content/images/Insecticide-Toxicity-in-Cats-Lecture-Notes.pdf


Scientist holding a petrie dish

Tetrachlorvinphos (TCVP) (organophosphate):  An organophosphate insecticide for animals and their living areas.  It kills fleas, ticks, flies, lice and larvae. Organophosphates are chemical ingredients processed in a specific way differently from other insecticides.

Tetramethrin (Pyrethroid Family): A powerful broad-spectrum, first-generation synthetic insecticide.136https://en.wikipedia.org/wiki/Tetramethrin137 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/tetramethrin[/mfn]137 https://archive.epa.gov/pesticides/reregistration/web/pdf/tetramethrin-red.pdf138https://echa.europa.eu/substance-information/-/substanceinfo/100.028.829139 https://pubchem.ncbi.nlm.nih.gov/compound/Tetramethrin#section=Formulations-Preparations

drawing of chemical lab test equipment

What Is a Flea? What Does It Look Like?How to Kill Fleas on Kittens, Senior & Sick Cats
Ways to Get Rid of Fleas on Healthy Cats!Is a Flea Treatment with Chemicals Safe for My Cat?
Getting Rid of Fleas…For Cats Only!What is a Natural Flea Treatment for My Cat?
Natural Flea Remedies You Can BuyFlea Control, the Homemade Way…
What Are Essential Oils…Do They Kill Fleas on Cats? What Is a Tick?
Cat Flea Collars


Sources used on this website are either primary or secondary.  Primary are always preferable and have the most reliable information because primary sources are original and directly referenced. Scientific abstracts and data are good examples of primary sources.

Secondary sources are weaker because they usually consist of opinions or articles that give no sources of their own, although sometimes they refer to primary sources. Thus, when I use secondary sources most are those with some authority, such as veterinarian or cat behaviorist books and articles.

List of Sources

See here for the list of all sources used on this page…

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