Permethrin
Cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, (3-phenoxyphenyl)methyl ester
What does permethrin actually do?
Permethrin is not a skin repellent. It's an insecticide you apply to clothing and gear, where it kills or knocks down ticks and mosquitoes on contact for about six weeks or six washes. Paired with a skin repellent, treated clothing is the most effective tick defense system available to consumers.
When to choose it: Boots, socks, pants, and packs for hikers, hunters, and anyone in tick country. An RCT among outdoor workers showed major reductions in tick bites.
A synthetic pyrethroid for treating clothing and gear, not skin. Bonded to fabric it kills ticks and mosquitoes on contact for weeks at a time, which makes treated clothing plus a skin repellent the strongest tick defense a consumer can assemble.
How it works
Permethrin binds the sodium channels in insect and tick nerve cells and holds them open, so an arthropod that crosses treated fabric is paralyzed and dies. It acts by contact on cloth rather than by scent, and it is not meant for skin.
The evidence
The clearest data are for ticks. A two-year randomized, placebo-controlled, double-blinded trial of factory permethrin-treated clothing among outdoor workers in a Lyme-endemic region recorded a large drop in tick bites versus untreated clothing.
- Emergence and spatial distribution of knockdown resistance in a suburban population of Aedes albopictus2026OtherWell-supported evidence
Longitudinal field-genetic surveillance study tracking how quickly pyrethroid knockdown-resistance (kdr) spread through a suburban Aedes albopictus (Asian tiger mosquito) population. Researchers genotyped 2,669 mosquitoes trapped across Wake County, North Carolina from 2016 to 2024, using an allele-specific PCR melt-curve assay for the F1534S sodium-channel mutation and a Wright-Fisher approximate Bayesian model to estimate the strength of selection. This is a resistance-monitoring study, not a repellent efficacy trial, so it carries no protection-time measurement.
- Protective effectiveness of long-lasting permethrin-impregnated clothing against tick bites: a randomized controlled trial among outdoor workers2020RctDefinitive evidence
A randomized, placebo-controlled, double-blinded trial testing whether factory permethrin-treated work clothing actually cuts tick bites for people exposed on the job: outdoor workers in Rhode Island and southern Massachusetts, a high-Lyme region. One group wore treated clothing, the other identical untreated clothing, and neither the workers nor the researchers knew which was which.
Products using it
Repel
Repel Propane Insect Fogger (Model 190397)
Tetramethrin 0.10% · Permethrin 0.25%
Coverage & effectiveness
Black Flag
Black Flag Electric Insect Fogger (Model 190107)
Tetramethrin 0.10% · Permethrin 0.25%
Coverage & effectiveness
Common misconceptions
Myth: “Permethrin spray works like bug spray.”
Reality: No. It degrades quickly on skin and isn't labeled for it. Its job is on fabric, applied the night before and allowed to dry.
Myth: “It's too dangerous to use at all.”
Reality: Dried-on-fabric permethrin has a strong human safety record (it's also a prescription scabies treatment). The real cautions: keep wet spray away from cats, and away from waterways.
Regulatory notes
Source: EPA SRS active ingredient list export. Minimum risk (25(b)) status is applied separately when applicable.
Safety notes
Dried on fabric, permethrin has a long human safety record and is used medically against scabies and lice. Wet spray is a different matter: it is highly toxic to cats and to fish, so treat clothing outdoors, let it dry fully, and keep it away from cats and waterways.
Frequently asked questions
How long does permethrin-treated clothing last?
Self-treated clothing holds about 6 weeks or 6 washes; factory-treated garments survive dozens of washes.
Is permethrin safe around pets?
Dried fabric is fine. Wet permethrin is highly toxic to cats, so treat and dry clothing away from them.