Permethrin is a synthetic chemical belonging to the pyrethroid class, structurally similar to natural insecticides found in chrysanthemum flowers. This compound is registered as an insecticide designed to kill insects upon contact or exposure, not primarily to repel them like traditional formulas containing DEET. While it may cause insects to avoid treated surfaces, its main function is to deliver a lethal dose to mosquitoes and other pests that land on the material. This distinction changes how the product should be used for effective personal protection.
How Permethrin Affects Mosquitoes
Permethrin functions as a potent neurotoxin that disrupts the mosquito’s nervous system. The chemical targets the voltage-gated sodium channels located in the insect’s nerve cell membranes. Normally, these channels open and close rapidly to transmit nerve impulses, but permethrin binds to them and forces them to remain open.
This prolonged opening leads to a continuous influx of sodium ions, preventing the nerve cells from repolarizing correctly. The result is hyperexcitability, uncontrolled nerve firing, and a loss of motor function. This disruption manifests as rapid paralysis, often called “knockdown,” which quickly leads to the mosquito’s death.
The killing effect provides protection, differentiating it from true repellents that confuse the mosquito’s sense of smell. While some insects may be deterred from landing, the primary benefit is that any mosquito making contact with the treated fabric will be incapacitated. This contact action ensures mosquitoes are killed before they can bite the person wearing the treated clothing.
Proper Use on Clothing and Gear
Permethrin is designed for application to clothing and gear, and should never be applied directly to the skin, unlike traditional insect repellents. The treatment bonds to fabric fibers such as shirts, pants, boots, and mosquito nets, turning them into long-lasting insecticidal barriers. This method is effective because the insect only needs to touch the treated surface to absorb a lethal dose.
Consumers can purchase factory-treated clothing or apply the product themselves using an aerosol spray or a soak method. Factory-applied treatments, often patented, can remain effective through up to 70 washings, offering durable protection. Do-it-yourself aerosol spray applications, typically using a 0.5% concentration, last for about four to six washes before reapplication is necessary.
When applying a spray, the item must be hung outdoors in a well-ventilated area and saturated until fully moist, but not dripping wet. The material must then be allowed to dry completely, ideally in a shaded area, which can take several hours. Treating gear like tents and backpacks is also recommended, as permethrin does not stain or damage most fabrics.
Safety Considerations and Precautions
When permethrin is used as directed on clothing and gear, its toxicity risk to humans is low. Once the treated clothing has dried, the chemical is fixed to the fabric fibers, and human exposure is minimal. However, it is important to avoid applying the product in an enclosed space to prevent inhalation of the wet spray.
A precaution must be taken regarding household pets, as permethrin is highly toxic to cats. Cats lack the specific liver enzymes necessary to metabolize and eliminate the compound, which can lead to severe neurological symptoms like tremors and seizures, often proving fatal. Owners must ensure cats are kept away from wet, recently treated items and any area where the application took place.
Permethrin is also highly toxic to aquatic life, including fish and aquatic invertebrates, even at low concentrations. When performing a do-it-yourself application, steps should be taken to ensure the product does not contaminate nearby bodies of water. The environmental impact and the danger to cats underscore the necessity of strictly following all product label instructions.