The Ultimate Guide to Fleas : For Cats

Updated: Apr 2, 2020


There are over 2000 species of fleas (1) with the most common being Ctenocephalides felis or the cat flea (2). Let’s face it, fleas are a pain in the ass. I would put them in the same category as cockroaches. They seem to never die and are resistant to many things that should eliminate them. Flea Life Cycle

There is a common set of myths that if you keep your house clean, don’t have animals that go outside, don’t have carpeting in your home, have animals that are raw fed and that you can’t get fleas in cold weather. THIS IS ALL WRONG. Humans can bring eggs into their home on their shoes for example, they can live in your yard and fleas can find refuge in your comfy home hoping to find a host.

While you may only see a few adult fleas, this is only part of the flea population, 1-5%. 8-10% of the population is only in the cocoon stage, 35-37% is in the larval stage and 50-54% are flea eggs (3). Adult fleas typically live for 60-100 days laying approximately 10-50 eggs each day (4). They do require ideal conditions but laying dormant (5) until warm, more humid conditions aren’t out of the question. 75-95 degrees and 60-85% humidity often are the preferred conditions (6).

Adults lay eggs on their host where they develop into larvae and pupae (7). In the summertime eggs hatch much quicker in less than 24 days while in the winter they can take up to 200 days to hatch (8). The larvae typically take 1-10 days to appear but on average lasts 5-11 days. Followed by the pupal stage which lasts for 5-9 days on average but could remain in this stage for 6 or more months until conditions are ideal (9,10). If temperatures are cold and dry, things will progress slower versus warm and humid environments. In addition to environmental conditions in humidity and temperature, other influences include vibrations, increases in carbon dioxide and body heat that are emitted by your companion animal, inspiring the pupae to exit the cocoon and find a host (3, 7).

So in short:

Adults lay 10-50 eggs per day and live for about 60-100 days

The Larval Stage is 5-11 days

The Pupae Stage is 5-9 days and can live in this cocoon for days up to 6 months or more.

Commercial Chemical Flea Treatments

Typically the first thought is two-fold 1) treat all year round whether you have fleas or not so you (hopefully) never get them and 2) treat with a chemical-based product often easily obtained from your veterinarian.

Below is a list of the most common and most widely available flea products available on the market not only through veterinarians but online pharmacies and pet suppliers as well.

  • Activyl (topical)

  • Adams Plus (topical)

  • Advantage Kitten (topical)

  • Bio Spot (topical)

  • Bravecto (topical)

  • Capstar (oral)

  • Catego (topical)

  • Cheristin (topical)

  • Comfortis (oral)

  • Easy Spot (topical)

  • Frontline Gold (topical)

  • Frontline Plus (topica)l

  • Hartz Ultraguard Plus (collar)

  • On Guard (topical)

  • Pet Armor (topical)

  • Revolution (topical)

  • Sentry Fiproguard (topical)

  • Sentry Purrscriptions (collar)

  • Seresto (collar)

  • Shield Tec (topical)

  • Vectra (topical)

  • Virbac (topical)

  • ZoGuard Plus (topical)

All of these products contain chemical agents that are designed to kill and inhibit fleas, ticks and/or mosquitoes, typically “protecting” your companions for up to 30 days. Many of these products do not repel these pests. Often the product is absorbed through the skin or orally ingested making its way into the bloodstream and then into the skin. Fleas must bite your companion for the product to work. This is the only way for the product to affect the fleas therefore your companion will still be bitten and any potential disease that can be contracted from fleas (7, 11, 12, 13, 14, 15, 16) can still afflict your companion. Many of these products cannot be safely used on pregnant females or kittens younger than 8 weeks old, some 12 weeks and others younger than 6 months of age. Each product is different in regards to what age they can be given and the ingredients they contain so make sure you are aware of ingredient lists and label instructions. One concern for cats is the use of pyrethroids and pyrethrin (which are in the pyrethroid family) in products. Pyrethrins are produced by the flowers of pyrethroids such as Chrysanthemums. Pyrethroids are derived from pyrethrins and are a synthetic anti-parasite and insecticide (17). They affect the nervous system in insects, causing muscle spasms, paralysis, and death (18). Ok so we need to get a little sciency about pyrethrum. In the natural form, pyrethrum extract is made of six esters (19), a type of organic compound that reacts with water to create alcohols and other organic and inorganic products (20). The synthetic type only has one. Natural or synthetic, the liver needs to break down the compounds however this can result in a hospital visit or death due to the increase in toxic levels, a risk for animals and humans that use these products (21, 22, 23).

In one case, an 11 year old girl was washing her dog with a shampoo containing 0.2% pyrethrin. The girl suffered and acute asthma attack and unfortunately died two-and-a-half-hours after being exposed to the shampoo (24). These are extremely dangerous to cats especially because cats cannot properly metabolize these chemicals. Typically the liver and an enzyme called plasma esterase breaks down the insecticide and then metabolizes and excretes it via the urine. Unfortunately cats either do not have or do not produce enough of the proper enzyme in the liver resulting in build-up and toxicity in the body (25, 26). Because it can dissolve in fat, pyrethrins can build up in the nervous tissues but at 1.5-7.5 times what is in the plasma (27). This also means they are rapidly absorbed. In fact, pyrethroid toxicity is one of the most common toxicities seen in veterinary clinics when it comes to cats (28). Pyrethrins especially Type I adhere to sodium channels located on nerves affecting how the channels operate. This causes a reversed extended duration of sodium flow resulting in repetitive nerve flow (29) which then cause signs of neurological distress (30).

On many product labels, although not always the case, you often will not find pyrethrin listed however there are many ingredients that are pyrethroids. These include but are not limited to:

  • Allethrin

  • Bifenthrin

  • Cyfluthrin

  • Cypermethrin

  • Cyphenothrin

  • Deltamethrin

  • Esfenvalerate

  • Etofenprox

  • Fenpropathrin

  • Fenvalerate

  • Flucythrinate

  • Flumethrin

  • Imiprothrin

  • lambda-Cyhalothrin

  • Metofluthrin

  • Permethrin

  • Prallethrin

  • Resmethrin

  • Silafluofen

  • Sumithrin

  • tau-Fluvalinate

  • Tefluthrin

  • Tetramethrin

  • Tralomethrin

  • Transfluthrin

In general, the chemical ingredients found in flea products aren’t good for our sensitive feline friends. The following is a list of the ingredients found in the above-mentioned flea products, what they do and the reactions they can and often cause.

(S)-Methoprene-a pesticide product that mimics a hormone that regulates growth in common pests. It prevents growth, shedding, moling, egg release and hatching. Skin, eye, respiratory irritation, vomiting, pupil dilation, behavior changes as well as breathing and movement. Can be stored in the liver, kidneys, lungs and blood, or be eliminated in urine and feces (31).

Allethrin-the first pyrethroid synthesized from chrysanthemum flowers that paralyzes the nervous system. Highly toxic to cats. Toxic via skin absorption and ingestion, itching, burning, tingling, numbness, warmth, nausea, vomiting, diarrhea, hyperexcitability, incoordination, tremors, convulsive twitching, bloody tears, incontinence, muscular paralysis, coma, mutagenic (32, 33, 34, 35, 36).

Amitraz-insecticide and repellent. Works by over exciting and paralysis that leads to death specifically for those in the spider families. Low blood pressure and pulse, hypothermia, lethargy, reduced appetite, vomiting, increased blood sugar and digestive issues, skin irritation (itching, eczema, alopecia) conjunctivitis, dilated pupils, seizures, coma, drooling, bloating, collapse. Classified as likely or possible carcinogen by the EPA (37, 38, 39).

BHT- Butylated Hydroxytoluene is a preservative used to prevent oxidation and rancidity of fats (40). Lower doses produced increased liver weight and decreased the activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue (41, 42, 43, 44).

Bifenthrin-an insecticide in the pyrethroid family. It is an active ingredient of Talstar, Capture, Ortho Home Defense Max, and Bifenthrine. Vomiting, diarrhea, reduced activity, twitching ears, flicking paws, drooling, hyperactivity, incoordination, depression, dilated pupils, chewing, head bobbing, partial paralysis, tremors. Classified as likely or possible carcinogen by the EPA (45).

Cyfluthrin-an active ingredient in Baygon, dichlorovinyl derivative of pyrethrin. Skin, eye and respiratory irritation, toxic if ingested, vomiting, burning of the mouth, dizziness, fatigue, nausea, abnormal walking, drooling, hyperactivity, loss of weight, fluid in the lungs, seizures, coma, death (46).

Cypermethrin- is an insecticide in the pyrethroid class that acts on the stomach as a poison and attacks the nerves paralyzing or causing the pest to die. Toxic to cats. Includes isomer alpha-cypermethrin, dichlorovinyl derivative of pyrethrin. Vomiting, incoordination, tremors, loss of movement, convulsions, diarrhea, weight reduction of organs. Classified as likely or possible carcinogen by the EPA (47).

Cyphenothrin-a synthetic pyrethroid insecticide causing hyperactivity and paralysis that leads to death. Toxic to cats. Resistance is common. Ataxia, hyperactivity, tremor, skin sensitivities, lethargy, drooling, vomiting, diarrhea, urinary incontinence, fever, low body temperature, difficulty breathing, disorientation, cramps, spasms (48).

Deltamethrin-An insecticide from the pyrethroid family that disrupts the nervous system. Dibromovinyl derivative of pyrethrin. Vomiting, drooling, incoordination, muscle tremors, skin sensations like biting, scratching, licking the area (49).

Dinotefuran-An insecticide that causes hyperactivity, paralysis than death of the flea. Drooling, gagging, vomiting, agitation, pruritus, pain (50).

Esfenvalerate-A synthetic pyrethroid insecticide that causes paralysis in fleas leading to death. Muscle incoordination, tremors, convulsions, nerve damage, weight loss, nausea, vomiting, weakness, eye irritant, maternal toxicity in the second generation (51, 52, 53, 54, 55).

Etofenprox-A pyrethroid derivative developed and imported from China that causes hyperactivity, paralysis then death of the flea. Respiratory distress, seizures, sores/lesions, vomiting, lethargy, liver damage, loss of appetite, heart failure, carcinogenic (56,57).

Fenpropathrin-A pyrethroid insecticide known to be a dopamine neurotoxin, harmful to the skin, fatal if inhaled, toxic if ingested. Eye and skin irritation, sound or touch irritability, prickling, tingling, creeping skin, numbness, dizziness, nausea, vomiting, diarrhea, drooling, fatigue (58).

Fenvalerate-A synthetic pyrethroid insecticide causing hyperactivity and paralysis that leads to death. Restlessness, tremors, piloerection, diarrhea, abnormal walking, skin irritant, death.

Fipronil-A broad spectrum insecticide that causes hyperexcitability that affects the nerves and muscles and GABA receptors. Sweating, nausea, vomiting, abdominal pain, dizziness, agitation, weakness, seizures, carcinogenic. Classified as likely or possible carcinogen by the EPA (59).

Flucythrinate-A pyrethroid insecticide that acts on contact and in the stomach. Eye and skin irritation, convulsions, motor impairment, skin lesions, weight retardation, heart arrhythmias, slowing of the heart, lactation and litter mortality increased ( 60, 61, 62).

Flumethrin-A pyrethroid insecticide that cause hypersensitivity, paralysis than death. High resistance is seen with several pests including fleas. Skin lesions, ataxia, hyperactivity, tremors, paresthesia, lethargy, drooling, vomiting, diarrhea, urinary incontinence, fever, lowered temperature , impaired breathing, incoordination, cramps, spasm (63, 64, 65).

Fluralaner-Oral insecticide which inhibits the nervous system of fleas via GABA and glutamate channels (66, 67). Convulsions, hair thickening, weight loss, vomiting, skin irritation, eye irritation/damage, respiratory sensitivity, organ toxicity, germ cell mutagenicity, genetic defects, reproductive toxicity, lethargy, lesions, diarrhea, itching, decreased appetite (68, 69, 70).

Glycol Ether-A group of solvents often used in paints and cleaners responsible for keeping other ingredients stable. Hazardous on the skin and when breathed in. Over exposure can cause anemia, intoxication, eye irritation, low level exposure shows birth defects and damage to the sperm and testicles, low birth rates, liver cancer (71, 72).

Imidacloprid-An insect neurotoxin affecting the central nervous system. Vomiting, drooling, incoordination, tremors, lethargy, skin reactions, convulsions, breathing impairment, cramps, thyroid impairment (73).

Imiprothrin- A pyrethroid derivative causing paralysis to pests like fleas. Eye irritation, weight loss and reduction in appetite, developmental and reproductive toxicity (74, 75).

Indoxacarb- An oxadiazine pesticide that works by blocking neuronal sodium channels. Nasal and eye discharge, immobility, lethargy, tremors, spasms, drooling, rapid weight loss, paralysis, death (76).

Isopropyl Alcohol-A type of alcohol (common rubbing alcohol) that kills and repels fleas. Incoordination, vomiting, lethargy, tremors, drooling, weakness, collapse, decreased respiratory rate, low blood sugar.

lambda-Cyhalothrin-A synthetic pyrethroid insecticide causing hyperactivity and paralysis that lead to death of the flea (77, 78).

Metofluthrin-A pyrethroid insect repellent primarily to repel mosquitos. Vomiting, increased organ weight, tremors, hyperactivity, abnormal vocalization, ataxia , convulsions, hypothermia, abnormal movements, drooling, kidney lesions, fatty liver disease, death (79, 80).

Nitenpyram-An insecticide that blocks neural signals in the nervous system leading to paralysis and death. Increased vocalization, obsessive grooming, vomiting, diarrhea, appetite loss, drooling, trembling, increased heart rate and seizures (81, 82).

Permethrin- Anti-parasite and insecticide in the pyrethroid family. It affects the nervous system in insects, causing muscle spasms, paralysis and death. Sichlorovinyl derivative of pyrethrin and most widely used pyrethroid. Flicking paws, twitching ears or skin, rolling on the ground, drooling, lip smacking, anxiety, abnormal walking, tremors, seizures, death. Classified as likely or possible carcinogen by the EPA (83).

Prallethrin-A pyrethroid insecticide and repellant generally used against mosquitos. Reduced motor activity, tremors, effects of the thyroid, heart, kidney and liver, drooling, exaggerated reflexes, decreased birth weights, acute dermal, oral and inhalation toxicity (84.85).

Pyriproxyfen-A pesticide that mimics a natural hormone in pests that disrupts their growth. Reduced activity, gained weight, diarrhea, abnormal breathing, loss of muscle control, vomiting, incontinence, increased cholesterol, increased liver weight, other effects on the liver and kidney, reduced birth weights, skeletal and digestive abnormalities, potential effects on androgen and thyroid pathways (86).

Resmethrin-A pyrethroid insecticide that works by interfering with a nerve cell's ability to send a normal signal. An active ingredient of Scourge. Numbness, itching, burning, tingling, incoordination, twitching, incontinence, seizures, eye irritation, liver enlargement, increased thyroid weight, behavioral changes, decreased blood glucose, premature/stillbirths, decreased birth weight , skeletal abnormalities, adverse reactions in the central nervous system (86, 87, 88, 89).

Selamectin-A topical parasiticide to kill and repel fleas causing paralysis, muscle contractions and death. Irritability, hair loss, drooling, rapid breathing, lack of coordination, vomiting, diarrhea, fever, tremors, loss of appetite, allergic reaction, hives (90).

Silafluofen-A pyrethroid insecticide. Excessive drooling, agitation, restlessness, vomiting, loss of coordination, difficulty in moving like jumping, standing, walking, shaking, twitching, tremors, shaking, abnormal breathing (91).

Spinetoram-An antiparasitic that acts on GABA and nicotinic receptors. Lower thymus weights, arteritis, bone marrow necrosis, reproductive effects including ovarian follicles, resorption, difficult births (92, 93).

Spinosad-An antiparasitic that acts on GABA and nicotinic receptors that is made by a soil bacterium . Irritation, redness, vomiting, gland and immune cell effects, increases in protein and fat in the blood, low body weight, organ effects, abnormal vaginal bleed, abnormal labor, abortions (94).

Sumithrin-Also know as Phenothrin is a pyrethroid insecticide. An active ingredient of Anvil. Drooling, depression, ear twitching, facial twitching, tremors hyperthermia, vomiting, anorexia, seizures, death (95).

tau-Fluvalinate-A synthetic pyrethroid. Conjunctival discharge, swelling and redness, vomiting, diarrhea, dehydration, neurological abnormalities, maternal and fetal toxicity, impaired learning, temporary memory impairment, mutation, skin irritation (96).

Tefluthrin-One of the most toxic pyrethroids. Tremors, increased thyroid weight , ataxia, neurological effects, skin irritation, behavioral changes, death (97, 98).

Tetramethrin-A potent synthetic insecticide in the pyrethroid family. Tremors, seizures, incoordination, twitching, excessive drooling, weakness, agitation, vomiting, diarrhea, shock, respiratory difficulty. Classified as likely or possible carcinogen by the EPA (99).

Tralomethrin-A pyrethroid insecticide that cause spasms, paralysis than death. Flicking tail, twitching ears and skin, shaking paws, abnormal movement or behavior, tremors, seizures, hypoglycemia, kidney failure, hyperthermia, drooling, stomach/gastric irritation, death (100).