[pct-l] Mosquitos, Permethrin and leave no trace

[Marr, Eli B]

There has been a lot of talk about mosquitoes and using Permethrin as a repellent. Please read this so you can make an informed decisions on whether or not you want to use the chemical in your hike.

First let me say I am a cancer researcher at one of the best Children's Hospital Research centers in the world. I am just a hiker doing my first thru hike on the PCT and am concerned about the environment and all of the great people I'm going to meet on my hike. This being said, here is what I have found about Permethrin:


Colombia gear and several other outfitters are selling anti-bug/insect blocker clothing. This clothing contains the chemical Permethrin as its active ingredient. You can also buy Permethrin at REI or other outfitter stores to treat your clothes, bags and gear with. Permethrin is EXTREMELY toxic to aquatic organisms and invertebrates and is labeled as a carcinogen by the EPA. Columbia states their insect blocker technology is completely safe and registered with the EPA without restriction. Let me give you a few quotes directly from the EPA website about Permethrin:

The Agency classified Permethrin as “Likely to be Carcinogenic to Humans”. This classification was based on two reproducible benign tumor types (lung and liver) in the mouse, equivocal evidence of carcinogenicity in Long- Evans rats, and supporting structural activity relationship information.

"The cancer risk estimates for adults exposed to surfaces treated with permethrin from directed surface sprays were above the Agency’s LOC." (Level of Concern: This is how the EPA rates products as potentially hazardous to people or the environment. Below LOC=Safe. Above LOC= not so safe)

"Permethrin is highly toxic to both freshwater and estuarine aquatic organisms. Most agricultural, public health, and down-the-drain scenarios modeled resulted in exceedances in the acute risk quotient (RQ) for freshwater and estuarine fish, invertebrates, and sediment organisms."

"All residential/recreational exposures are expected to be short-term in duration. Therefore, no intermediate-term (1-6 months) or long-term (>6 months) aggregate risk was assessed."

Although not on the EPA site Permethrin is highly toxic to some mammals like cats. They used it in flea and tick prevention until cats started getting sick and dying. No more Permethrin allowed on cats.


Though the concentration of Permethrin used by hikers is lower than the EPA's limit keep in mind their limit was set for SHORT TERM use only. They have done no studies whatsoever on how the chemical might effect say... hikers who wear a Permethrin covered shirt for 5 months on the PCT. I don't know about you but that makes me a bit nervous. Permethrin is only absorbed into the skin at about a 2% rate (not that high) and is broken down by the body over time. But it still makes me nervous. I will be using Permethrin on my thru hike. It's effective for repelling bugs and better than getting west nile virus from a mosquito. However I am NOT applying it to anywhere touching my skin. I'm putting it on my pack, parts of my hat and on sections of my tent but it is not touching my clothes.

For anyone following any guidelines for Leave No Trace: DO NOT WASH YOUR PERMETHRIN COVERED CLOTHES IN ANY NATURAL WATER SOURCES!!! It will directly harm the aquatic life. This has been proven through multiple studies conducted by the EPA and other research centers. The EPA has strict regulations on any release of Permethrin near water sources. If you Permethrin your shoes, pants or socks and walk through a stream it puts the Permethrin directly into the ecosystem. Please be respectful of our environment and help keep the PCT clean for future hikers.

Thanks for reading and good luck to everyone! I leave for the trail in a few days.