Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Pyrethroids: Not as safe as you think

©2000 Melissa Kaplan


What are the pyrethroids?
Pyrethrin is one of two liquid esters derived from Pyrethrum (feverfew) (C21H28O3 or C22H28O5) that are used as insecticides. Pyrethrum, a nonvolatile hydrocarbon related to kerosene, is a similar insecticide derived from and chrysanthemum flowers.

The fact that they are derived from plants causes some people to think - a point played up by companies using this toxin in their products - that they are safe. Lots of plants are toxic, some in small quantities, others in large. Just because it comes from something lush and ornamental does not mean it can't be lethal. Oleander, azalea, mistletoe, and foxglove are just a few of the pretty - and highly toxic - plants with which we live.

Permethrin is a synthetic pyrethrin (C21H20Cl2O3). In other words, it is a man-made poison that is a copy of two poisons found in plants.


Brand Names
When chemical manufacturers make permethrin or extract pyrethrin for use in their own products or for sale to other companies to use as an ingredient in other products, their "brand" of pyrethrin or permethrin is given a unique name. Some of the names you may see on such products include:












Cyclopropanecarboxylic acid, 3-(2,2-dichlorethenyl)-2,2-dimethyl-, (3-phenoxyphenyl)methyl ester

Cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl-2,2-dim


The use of these insecticides are wide spread, including:

Ectoparasiticide: It has a potential application for forest protection and vector control for the control of noxious insects in the household and on cattle, for the control of body lice, and in mosquito nets.

Nematocide, Acaricide: Control of larvae (and also adults and eggs) of chewing lepidopterous and coleopterous insect pests on pome fruit, stone fruit, berry fruit, citrus fruit, vines, olives, vegetables, cereals, maize, oilseed rape, cotton, tobacco, soya beans, and in conifer nurseries; whiteflies and other glasshouse pests on glasshouse cucumbers, tomatoes, and ornamentals; and sciarid flies and phorid flies on mushrooms.

Also used for control of crawling and flying insects (e.g. flies, ants, fleas, cockroaches, silverfish, etc.) in public health, and in agricultural premises including animals houses; and as an ectoparasiticide on animals.

Widely used in home and garden pest sprays and in schools, both in the buildings and on the grounds.

To ensure long-lasting effects, the pyrethroid may be mixed with a fixative to make it stay on plants and soil longer, and other chemicals, such as piperonyl butoxide, which prevent the insects from detoxifying, and "inert ingredients". One of the problems is that manufacturers are not required to list the inert ingredients - even though they may themselves be highly toxic or cause know allergic and other reactions in organisms exposed to them - such as you, your children, and your pets.

Some insects have developed ways to detoxify the naturally occurring pyrethrums encountered when feeding on the nectar of feverfew and chrysanthemums, a not uncommon adaptive response. Unfortunately, while insects and plants have had millions of years to work out these survival pathways, we humans haven't.

An increasing number of insects have developed high levels of resistance to pyrethroids, such as cockroaches, head lice, and tobacco budworm, pear psylla, fall army-worm, German cockroach, spotted tentiform leafminer, diamondback moth, house fly, stable fly, head lice, and tobacco budworm. Many of these species are resistant to more than one pyrethroid. Because insects reproduce - and adapt - far more quickly than do vertebrates, they are far better able to evolve defenses against the toxins we throw at them, resulting in an ever expanding range of poisons developed and thrown into our environment.

Pyrethroids, like all toxins, are indiscriminate: they affect all the organisms who come into contact with them in the air, on plants, on the ground, in the soil, and in the water. While your local grower - or you - may be applying it to deal with a specific pest, the products affect everything around it. And, since particulates are easily airborne, they travel, often great distances, from the actual point of application.


Side Effects

Inhalation: coughing, wheezing, shortness of breath, runny or stuffy nose, chest pain, or difficulty breathing.

Skin contact: rash, itching, or blisters.

Long term effects: disrupts the endocrine system by mimicking the female hormone, estrogen, thus causing excessive estrogen levels in females. In human males, its estrogenizing (feminizing) effects include lowered sperm counts. In both, it can lead to the abnormal growth of breast tissue, leading to development of breasts in males and cancerous breast tissue in both male and females.

Neurotoxic effects include: tremors, incoordination, elevated body temperature, increased aggressive behavior, and disruption of learning. Laboratory tests suggest that permethrin is more acutely toxic to children than to adults.

Other: A known carcinogen. There is evidence that pyrethroids harm the thyroid gland. Causes chromosomal damage in hamsters and mice; deformities in amphibians; blood abnormalities in birds.


Piperonyl butoxide:
Skin Contact: skin irritation.

Eyes: eye irritation.

Long term effects: A known carcinogen.

Inert Ingredients: Some known ones include:

Xylenes (agricultural insecticides such as Pounce, Ambush 2E and Ambush 50): eye and skin irritation, headaches, nausea, confusion, tremors, and anxiety in exposed humans. In laboratory tests, xylenes have caused kidney damage, fetal loss, and skeletal anomalies in offspring.

Methyl paraben (head lice cream rinse Nix; regulated as a drug not as a pesticide): a skin sensitizer, causes eye, skin, digestive, and respiratory irritation.

Dimethyl ether (household insecticides such as Flea-B-Gon Total Flea Killer Indoor Fogger and Ortho Total Flea Control 2):. causes respiratory, skin, and eye irritation and depresses the central nervous system. It is also a severe fire hazard.

Butane (household insecticides such as Raid Yard Guard Outdoor Fogger V and Off Yard and Deck Area Repellant) : “extremely flammable” and short-term exposure causes irritation, nausea, drowsiness, convulsions, and coma.

So, what's the big deal?
While pyrethroids may be amongst the least toxic of insecticides, they are an excitatory nerve poison, acting upon the sodium ion channels in nerve cell membranes:

  • by sending a train of impulses rather than a single one, they overload the pathways, blocking the passage of sodium ions across cell membranes; similar in action to organophosphates (which include the now banned DDT); inhibits ATPase, which affects the release of acetylcholine, monoamine oxidase-A and acetylcholine;
  • inhibits GABAa receptors, resulting in convulsions and excitability (and more 'minor' problems such as sleep disorders);
  • known to be carcinogenic;
  • liver damage
  • thyroid function
  • cause chromosomal abnormalities in mice and hamsters;
  • are highly toxic to insects, fish, and birds;
  • mimic estrogen, leading to estrogen dominant health problems in females and feminizing effects in males, including lowered sperm counts and abnormal breast development;
  • sublethal doses have produced a wide array of abnormal behaviors, including aggression, and disruption in learning and learned behaviors

So, what's the alternative?
The alternative depends on what you are trying to do. In the case of commercial growers, gardens, schools, there in a growing body of information on Integrated Pest Management (IPM). Look for related websites using such meta-search engines such as Google, Teoma and Dogpile, or books at online sellers such as A1 Books,, Amazon US, Amazon UK, Barnes&Noble, Booksamillion, and

In the home, there are a wide range of non-toxic alternatives depending on what type of pest you are trying to control. Information and links on IMP and home alternatives can be found at my Natural Pest Control page and at the Institute of IPM site.

If you are trying to get rid of reptile mites, there are ways to do it without the use of any toxin on or near the reptile, or even in the enclosure. See my Reptile Mites article for more information.



The American Heritage® Dictionary of the English Language, Third Edition
Cancer WEB's On-line Medical Dictionary
Permethrin, from Insecticide Fact Sheet, Journal of Pesticide Reform, Summer 1998, Vol 18, No 214l
Spectrum Labs Chemical Fact Sheet

Related Articles/Sites

Pyrethrin: Common insecticide ingredient may cause allergic reactions

Pyrethrin and Pyrethroids Cause Adverse Reactions

A Little Less Green: Studies challenge the benign image of pyrethroid insecticides

Least Toxic Insect Control for Horses

The Effects Of Environmental Pollutants On North American Temperate Forests

Estrogen Dominance: Underdiagnosed health threat to women

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