What is Permethrin?

Many people ask “What is permethrin?” especially in Canada where there are restrictions on its sale and use. Author of the Canadian Rockies Trail Guide Brian Patton has written extensively on permethrin in Canada, and we thank him for the essay below.

Permethrin is a synthetic chemical insecticide that acts like a natural extract of the chrysanthemum flower. Repellents, like DEET and picaridin, disorient and repel insects, but permethrin attacks an insect’s nervous system and kills it. Permethrin-treated clothing and spray for self-treatment of clothing have proved to be very effective in stunning and repelling a wide variety of insects and ticks, and the diseases they can carry, such as Lyme disease.

Author Brian Patton takes notes during research on a mosquito-infested trail. CREDIT: Rhonda Allen

Lyme Disease

Lyme disease is a complex inflammatory illness caused by the bite of a black-legged tick infected with the grim Borrelia burgdorferi parasite. It is the most common tick-borne illness in Canada. In the Canadian Rockies, the risk of contracting Lyme disease is low as ticks present are wood ticks, but precautions should still be taken.

In many parts of Canada, including southern British Columbia, southern Manitoba, southern Ontario, and the Maritimes, Lyme disease has long been a threat, with the number of reported cases increasing from 144 in 2009 to over 2000 in 2022. As many cases go unreported or undetected, the number is probably higher.

Ticks and their potential to spread Lyme disease is an issue that affects not only hikers but anyone who spends time outdoors.

While I have no personal experience with Lyme, nearly everyone where I live in southern British Columbia knows someone who has been treated for the disease, or worse, wasn’t diagnosed early and now suffers with the chronic form.

Permethrin in Canada

In Canada, permethrin was approved for use in clothing worn by Canadian military personnel since the 1980s, but it wasn’t until May 2018 that Canadians were able to purchase clothing that is commercially treated with permethrin. Mark’s, was the first to offer a range of bug-repellant clothing in Canada. Factory treatment is considered effective for as many as 70 washings or, as is likely, for the life of the garment.

Permethrin spray designed for use on clothing (0.5% strength) is not permitted to be sold in Canada. The Public Health Agency of Canada here currently states “Permethrin products in the form of liquids or sprays for consumers to treat their own clothing are not approved for use in Canada.”

Permethrin spray could be ordered online for shipment from the U.S. to Canadian addresses a year or so ago, but not today. Though I’ve not seen any documentation, it appears the Canadian government is trying to stem the flow of permethrin spray into Canada.

Permethrin in the United States

In the United States, where Lyme disease is one of the fastest-growing infectious diseases, people defend themselves with permethrin-treated clothing and spray.

Factory-treated permethrin clothing has been sold commercially in the U.S. since 2003. I have used permethrin clothing sprays purchased in the U.S. However, as a hiker, I find it an expensive and fussy alternative to commercially treated clothing since you need to repeat the treatment every six weeks or so and take care with how treated items are laundered and stored.  I do keep a couple of cans handy for spraying hats, socks and pant legs.

In the U.S., you can purchase permethrin spray, which is applied to any clothing, however, the level of protection is usually listed as six weeks or six washings. Sawyer spray products are popular. Permethrin should not be sprayed directly on the skin.

More Sources of Permethrin and Lyme Disease Information

If you are interested in Brian Patton’s other research and thoughts, click on the following links:

Ticks, permethrin, and Canadian hypocrisy

Permethrin-treated clothing arrives in Canada

Mark’s permethrin-treated clothing.

CBC interview including quotes form Brian Patton

The Government of Alberta offers up a Lyme disease and tick surveillance page.

For information on permethrin-treated clothing in Canada go to the Public Health Agency of Canada website. The same agency provides information on various repellents here. Somewhat ironically, while permethrin is not widely available in Canada, the Canadian government recommends permethrin for travellers on their website, stating “permethrin-treated clothing is effective” and that “a travel health clinic can advise you how to purchase permethrin and pre-treated gear before or during your trip.”

The Government of Canada updates Lyme disease data on this page of their website.

Vanessa Farnsworth’s personal memoir Rain on a Distant Roof: Personal Journey Through Lyme Disease in Canada (2013; ISBN: 9781927426234) explores the captivating but frightening story of Lyme disease in Canada. As a respected science writer affected by the disease, Farnsworth does a great job of describing her symptoms, confusing diagnoses, the lack of research, and problematic responses from all levels of government in how the disease is treated in Canada. She also maintains the website Lyme Disease in Canada, which is loaded with information on Lyme disease and has links to many reports.

The most recent report related to Canada on the subject was the 2022 study  Epidemiology of ticks submitted from human hosts in Alberta, Canada (2000-2019) by the University of Alberta. The article first appeared in the Emerging Microbes & Infections journal.

The U.S. Centers for Disease Control and Prevention (CDC) has a page dedicated to Lyme disease here. Also from the States, there is an EPA report on Repellent-Treated Clothing. The National Pesticide Information Center has a page dedicated to permethrin, although when we looked it hadn’t been updated for many years. This resource discusses what permethrin is, how it works, and the possible side effects on humans and the environment.

We thank Brian Patton, author of the Canadian Rockies Trail Guide for the content on this page.