By Dr. James Katz, MD, MPH
Just When You Thought you Could Go Outside — It’s Lyme Disease Season 2023!
Recently, three significant articles were published confirming the safety and effectiveness of permethrin treated clothing against Lyme disease. A two year study in Rhode Island among outdoor workers permethrin treated clothing reduced tick bites by 58%. The Army reported that permethrin treated clothing used in high heat and high humidity for extended periods increased permethrin excretion but had no ill health effects.
Beware this nearly invisible menace.
While Lyme disease cases are rising in the civilian population, the incidence is falling in active military units. What does the military know that your public health department does not?
The Military Learned Permethrin is Safe and Effective
The U.S. Army, in 1994, was confronted by a rising incidence of Lyme cases, and the conventional advice wouldn’t work for troops deployed in combat. Civilians are told to wear light-colored clothing, long-sleeved shirts, tuck pants into socks, stay in the middle of trails, and frequently apply DEET — and also to strip naked for a daily tick check. This is impractical even for casual hikers — it’s ridiculous for deployed troops. Additionally, the medical statistics don’t lie — these practices don’t work to prevent tick bites and infection.
The military needed a fail-safe approach, and they found the right weapon in a flower — chrysanthemums contain pyrethrum, a natural insecticide that kills ticks and mosquitoes.
If you plant chrysanthemums around the perimeter of your yard, when they start blooming in late summer, the number of ticks in your yard will drop. In 1973, chemist Michael Eliot modified pyrethrum to be stable in sunlight and named it permethrin. Two million pounds were manufactured last year for agricultural use, including treating fields on organic farms. It is the treatment of choice for scabies in infants and pregnant mothers. The Army asked the National Research Council to evaluate the safety of uniforms treated with permethrin.
The National Research Council’s concluded permethrin is safe. They projected that a soldier could wear his/her combat uniform 18 hours a day, seven days a week, for 35 years (230,000 hours) without toxicity. The NRC estimated the most frequent adverse effect in the 35 years would be an infrequent, self-limited rash.
The application of permethrin to clothing is undetectable. Hunters use it because it has no scent. It does not have a texture. Your children will not know you treated their favorite sneakers, socks, and blue jeans. I treated my daughter’s silk dress she wore to graduation and she was none the wiser. Home-treated garments remain protective for six washings.
Do not be put off by the warnings on a container of permethrin. The bottle is yellow and black, the same color scheme for roadside hazards, radioactive materials, and toxic waste. Really? There are no reports of respiratory, gastrointestinal, central nervous system, or cardiac sensitivity. The International Agency for Research on Cancer (IARC) found no evidence of carcinogenicity. The container has EPA warnings for agricultural strength permethrin. For human exposure, the EPA considers permethrin below its “Level of Concern.”
Permethrin is safe for humans and pets as sold for household use.
Cats have a reaction to 45% permethrin dog tick treatments. Dr. Charlotte Means at the ASPCA Animal Poison Control Center states. “It’s the dose that is the problem. The concentration of permethrin in household sprays is much lower — (40 times lower) typically less than 1 percent — and rarely causes problems with cats.”
For comparison purposes, permethrin is less toxic than Windex, Formula 409, or glue. Contrast this with suntan lotion, whose active ingredients — avobenzone, oxybenzone, octocrylene, and ecamsule — are absorbed into the skin at levels with possible cancer risk, says David Straus of the FDA.
Armor Against Ticks
Out in the field, the not-so-secret weapon is permethrin-treated fabric. In 2011, the German army introduced permethrin-treated clothing and reduced daily tick counts by 99%. In 2016, forest rangers in North Carolina had an 80% reduction of ticks seen on daily inspections. In 2018, the medical unit at West Point reported that active service members on field maneuvers 24 hours a day wearing permethrin-treated battle uniforms had half the risk of Lyme disease as their service family members who lived on base.
Lower the risk of Lyme by 50% — wear clothing treated with permethrin
You can wear clothing treated with permethrin, which will lower the risk of Lyme by 50%, Spray it on your children’s socks, shoes, and jeans and they will be none the wiser, but far safer. The same treated fabric kills mosquitoes, chiggers, mites, and many other insects. Your families are at risk for catching Lyme disease, which may lead to neurologic, muscular, immune, and cardiac complications that can last for years. I was taught never to accept a bet I could not afford to lose. Neither should you.
Spray clothes until damp and hang to dry. Clothes will remain protective for up to 6 washings. The gentle cycle is best since agitation can separate permethrin from the fabric. Or you can buy professionally treated clothing from suppliers such as LL Bean that last for up to 70 washes.
Golfers should spray permethrin on shoes, socks, and pants.
Permethrin treated clothing has even crossed from utilitarian clothing to fashion. Try this sample search to look for options.
Journal of Medical Entomology, Volume 57, Issue 5, 1 September 2020, Pages 1532–1538, https://doi.org/10.1093/jme/tjaa061
A Population-Based Investigation of Health Outcomes in Active Duty Army Service Members Before and After Requirement For Full-Time Wear of Permethrin-Treated Uniforms (USARIEM #17-22H; MRDC #M-10683)
Journal of Exposure Science & Environmental Epidemiology volume 30, pages525–536 (2020)