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Permethrin (Molecule of the Month for September 2002)

Insect Repellents



Ever wondered what's in bug spray and what drives those annoying bugs away? Well you're about to find out! The most common insecticide used in bug spray which is used on skin is a chemical called DEET also known as N,N-diethyl-m-toluamide. Another substance called Permethrin is often used on clothing, tents etc. There are also several natural insecticides like citronella, oils of cedarwood, lemongrass, peppermint, eucalyptus,soya bean oil, garlic and many more.

Blood sucking insects are attracted to many chemical and physical factors, including carbon dioxide, body heat, chemicals in sweat, and on the surface of skin, and odor of soaps and lotions we use.

Insect bites can be annoying for the itching they cause but they can also be harmful by transmitting certain diseases to humans. Malaria is the most commonly known disease caused by female mosquitos passing on the malaria virus into the blood stream of humans. It is estimated to cause approximately 3,000,000 deaths every year worldwide.

Insect bites can also cause allergic reactions in people which can, in rare cases be fatal.

Lyme disease is also one of the better known insect spread diseases. It is carried by ticks, most commonly known the deer tick. It is highly treatable in the early stages but if left undetected it can cause serious long term disabilities such as joints, severe headaches, and abnormal heart beat.

Ticks can also transmit Rocky mountain spotted fever, Colorado tick fever, and several forms of encephalitis.

Permethrin is a powerful, rapidly acting insecticide,similar in structure to natural pyrethrim insecticide derived from the crushed and dried flowers of the daisy Chrysanthemum cinerariifolium. Permethrin is a human-made synthetic pyrethroid. It does not repel insects like DEET does but works as a contact insecticide, causing nervous system toxicity that leads to the death or "knockdown" (out of the air) of the insect. The chemical is effective against mosquitoes, flies, ticks, and chiggers. Permethrin has low toxicity in mammals, is poorly absorbed by the skin, and is rapidly inactivated by ester hydrolysis - the insect can quickly get rid of it so it does not necessarily kill.

Permethrin should be applied directly to clothing or other fabrics such as tent walls or mosquito nets, not to skin. The spray form is nonstaining, nearly odorless, and resistant to degradation by heat or sun and maintains its potency for at least 2 weeks, even through several washings. In a field trial conducted in Alaska, persons wearing permethrin-treated uniforms and a polymer-based 35% DEET product had more than 99.9% protection (1 bite per hour) over 8 hours, even under conditions of intense biting pressures; unprotected persons received an average of 1188 bites per hour.

Permethrin should be applied to clothing or other fabrics. It is not intended for direct application to the skin. Once Permethrin has dried on the clothing it bind very strongly to the fibres and absorption through the skin is negligible.

Any permethrin that may get on the skin inadvertently is poorly absorbed (less than 2% of applied dose). It is rapidly inactivated by skin and liver esterases, its metabolites are then excreted by the kidneys. Occupational exposure to high doses of permethrin has been associated with symptoms of of itching, burning and numbness. Studies have shown permethrin not to be a human teratogen, mutagen, or carcinogen.

Permethrin is also environmentally safe as it is degraded by sunlight, its half life is less than 30 days in soil and the chemical is readily metabolized by soil microorganisms.

Formal Chemical Name (IUPAC)
3-(2,2-Dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid (3-phenoxyphenyl)methyl ester

Picture of Permethrin

click on the picture above to interact
with the 3D model of the
Permethrin structure
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Picture of Permethrin

C21 H20 Cl2 O3



Update by Karl Harrison
(Molecule of the Month for September 2002 )