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Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Permethrin as an Insect Repellent


A reader asks: “Do you feel that it’s worthwhile to purchase clothes that are pre-washed with permethrin? Is it a good idea to wash your hiking clothes with this prior to going on a hike? Should I buy permethrin soap and wash my kids with it?”

Please DO NOT wash your kids with permethrin. Permethrin, a synthetic pyrethroid based upon the naturally-occurring pyrethroids that are extracted from the East African pyrethrum flower (a chrysanthemum), is actually an insecticide; that is, permethrin-containing products kill insects and ticks. Because permethrin carries some potential toxicity to humans it should be used only on clothing (or on shoes, certain camping gear, bed nets, etc.), not on skin. For instance, permethrin is known to cause eye irritation if the chemical comes in contact with a person’s eyes. Although permethrin in a 5% lotion or cream is sometimes prescribed by physicians for application to skin for treatment of mite (e.g., scabies) infestation, these medical dermatologic preparations are not recommended for use as insect repellents. In the past, combination DEET-permethrin (the latter in very low concentration) soaps have been field tested for use as an insect repellent. While they have been acceptable to the persons that used them, a commercial product based upon this concept has not yet come to market.

There is ongoing discussion about the toxicities possibly associated with permethrin. These include potential cancer-causing potential, and perhaps abnormalities of the immune system. Properly used (e.g., applied to clothing and not directly to skin), it has not yet been directly linked with serious adverse effects upon humans, so it remains an effective barrier against insect-borne infections, , such as Lyme disease and West Nile virus. It is best used in combination in its application to clothing with an approved insect repellent (such as picaridin or DEET), when the latter is applied to skin.

There are many permethrin wash-in products for clothing on the market. An example is Sawyer Permethrin Wash-In Clothing Treatment™. Another is BUZZ OFF Insect Shield™ apparel, which is claimed to provide effective and convenient protection against mosquitoes, ticks, ants, flies, chiggers and midges. It is important to closely follow the label instructions. Clothing that is sold pre-treated with permethrin is often advertised to be effective (as a repellent) for up to 25 washings. If you are going to be in a high-risk (for an insect or arthropod bite capable of transmitting a disease) situation, to play it safe, the effectiveness should be assumed to begin to decrease after half the advertised allowable number of washings.

If you decide to apply permethrin spray to clothing, be certain to do the following (as recommended by the Connecticut Department of Environmental Protection):

1) Follow manufacturer’s instructions closely. Do not exceed recommended spraying times.
2) Treat clothing only. Do not apply to skin.
3) Apply the permethrin in a well-ventilated outdoor area, protected from the wind.
4) Only spray the permethrin on the outer surface of clothing and shoes.
5) Apply enough to lightly moisten the outer surface of the clothing item; it is not necessary to have the clothing soaked through (saturated).
6) Be certain to apply completely cover socks, trouser cuffs and shirt cuffs, where insects may attempt to crawl or fly through openings to your skin.
7) Hang treated clothing outdoors and allow to dry for at least 2 hours in non-humid conditions and for at least 4 hours in humid conditions.
8) Treat clothing no more often than every 2 weeks.
9) Launder treated clothing separately from other clothing at least once before re-treating.
10) Assume that your treated clothing is effective for repellency for 2 weeks or more. Wear it only when you need to repel insects and arthropods. Store it in a separate impermeable (to permethrin) bag when not in use.

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photo courtesy 3Dchem.com
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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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