Traveling abroad, I could only find cypermethrin available, so I started investigating if cypermethrin could also be used to treat clothes. Permethrin is the only pyrethroid approved for clothing by the EPA, but that doesn't conclude that other pyrethroids won't be effective.
For the same concentration, this research shows cypermethrin is more effective at killing mosquitoes: Permethrin as a residual lawn spray for adult mosquito control
“ Cypermethrin is yet another synthetic pyrethroid that, along with its emulsifiable concentrate formulations, are non-phytotoxic and have a very low order of dermal toxicity. It is considered to be among the least toxic of the synthetic pyrethroid insecticides. Alpha-cypermethrin is a racemic derivative of cypermethrin that is much more active for insecticidal activity than its parent compound. ” Insecticide-impregnated fabric and method of production, patent 2001
“ The insecticide solution contains a water-soluble cyclodextrin, a polymeric binding agent, and an insecticide. The preferred binding agent is polyvinyl acetate (PVA). The preferred insecticide is a pyrethroid. The cyclodextrin and insecticide in the insecticide solution bind together to form an inclusion complex, wherein the insecticide acts as a “guest molecule” nestling in the center of the hydrophobic interior of the water-soluble cyclodextrin. The fabric is impregnated by immersing the fabric in the insecticide solution and allowing the wetted fabric to dry. The inclusion complex binds to the fabric and allows the insecticide to remain attached to the fabric, even after several washes with a detergent and rinses, thereby prolonging the insecticidal effectiveness of the fabric.  Treatment of fabric with the insecticide composition described herein reduces the rate at which the insecticide is removed from the treated net during washings. Fabrics treated with the insecticide solution provide higher insect mortality than fabrics treated using solutions that lack the combination of a water-soluble cyclodextrin and a polymeric binding agent. Increased insecticidal effectiveness and wash-durability correlate strongly with the concentrations of cyclodextrin and binding agent in the solution used to treat the fabric. ” Insecticide-impregnated fabric and method of production, patent 2001
The following article covers the toxicity of pyrethroids, concluding that they are all mildly toxic to humans. No mention is made that one is more toxic than the other, although different concentrations should be used depending on the pyrethroid. Current Research on the Safety of Pyrethroids Used as Insecticides, Chrustek et al 2018. The same conclusion at Wikipedia. Nothing but vagueness from: Health Effects of Permethrin-Impregnated Army Battle-Dress Uniforms,1994.
“ …substantial uptake of permethrin from impregnated BDUs has to be assumed. However, since calculations reveal a maximum permethrin uptake clearly below the acceptable daily intake (ADI), health impairments are rather unlikely. ” Uptake of permethrin from impregnated clothing, Rossbach et al 2010
“ Our 2009 revised exposure and risk assessment evaluated multiple exposure scenarios for permethrin factory-treated clothing, including toddlers wearing or mouthing the clothing, and military personnel who wear permethrin-treated uniforms on a daily basis. All exposure scenarios showed that permethrin factory-treated clothing is unlikely to pose any significant immediate or long-term hazard to people wearing the clothing. ” epa.gov
“ Long-lasting permethrin-impregnated (LLPI) clothing retained permethrin and bioactivity against ticks after three months of use in real-world conditions. The estimated absorbed dosage of permethrin was well below the U.S. EPA level of concern, suggesting that LLPI clothing can be used safely by outdoor workers for tick bite prevention. ” Bioabsorption and effectiveness of long-lasting permethrin-treated uniforms over three months among North Carolina outdoor workers, Sullivan et al 2019
“ Those wearing permethrin-treated uniforms under the longer wear-time scenario (Study A) excreted significantly higher cumulative mean levels compared with those in Study B (3.29 times higher for 3PBA and 2.23 times higher for the sum of c/tDCCA (P≤0.001)). ” Permethrin exposure from fabric-treated military uniforms under different wear-time scenarios, Proctor et al 2013
“ Concerns about occupational exposure are increased because laundering is not completely successful in removing cypermethrin from clothing. Experiments found that up to 19 percent of residues remained after hand wash- ing, and up to 27 percent remained after machine washing.32,33 ”
“ When applying German Armed Forces licensing conditions, none of the four products available in the civilian market would completely meet all the necessary efficacy and safety requirements fulfilled by BDUs. Therefore, we strongly recommend standardized testing and licensing procedures for insecticide-treated clothing, with defined cutoff values for initial maximum and post-laundering minimum concentrations of permethrin as well as figures for permethrin migration rates, arthropod toxicity, homogeneity on fabrics, residual activity, and laundering resistance. ” Bioactivity and laundering resistance of five commercially available, factory-treated permethrin-impregnated fabrics for the prevention of mosquito-borne diseases: the need for a standardized testing and licensing procedure, Faulde et al 2016
“ Any pesticide product with permethrin won't do. Look for products with specific instructions for treating clothing. ” National Pesticide Information Center, 2019. The first rule of science is to state why. More than likely, they state this because products not for clothing are much higher in permethrin concentration. See NPIC on Wikipedia.
“ …mosquitoes are knocked down within 15 minutes after exposure to permethrin-treated clothing. ” Effectiveness of controlled-release personal-use arthropod repellents and permethrin-impregnated clothing in the field, Gupta et al 1984
“ 5% oregano and spearmint oils exhibit potential as natural clothing repellents, with an effective equivalence to 20% DEET. ” Essential oils as tick repellents on clothing, Soutar et al 2019
“ …permethrin has had limited general use due to its relatively short useful life of insecticidal action. The reason why the working life is short is that permethrin is decomposed in the presence of oxygen and ultraviolet light and turned into an inactive, non-insecticidal substance. … when McNally impregnated clothing with permethrin and amylopectin (which is a water-soluble form of starch), permethrin remained in the clothing for a much larger number of washing periods than clothing treated with permethrin alone. … another synergist, polyvinyl acetate, is more effective than amylopectin in retaining permethrin in the fiber material for a greater number of washing periods. ” Method and means for retaining permethrin in a washable textile material, patent 1995
“ Denim fabric having no washes and no light exposure showed the highest amount of permethrin. Washing and light exposure significantly reduced the ability of permethrin-treated fabrics to induce mosquito knockdown and/or mortality under the simulated conditions used for this test. Temperatures tested did not affect permethrin content or mosquito knockdown and mortality. ” Residual Effectiveness of Permethrin-Treated Clothing for Prevention of Mosquito Bites Under Simulated Conditions, Richards et al 2017
“ … a synergism between an amylopectin (a water soluble form of starch)-permethrin combination on textile fabrics to afford greater retention of permethrin in clothing through repeated wash cycles as compared to garments treated only with permethrin. Another example is disclosed in U.S. Pat. No. 5,503,918 wherein the addition of polyvinyl acetate as a binder for the permethrin dispersion preserves the effectiveness of the permethrin through more washings of the fabric than does the amylopectin used in the '298 patent. U.S. Pat. No. 5,631,072 discloses wash durable permethrin-treated garments prepared from a fabric that is either impregnated or single-side surface-coated with a dispersion of permethrin. In the case of impregnation, a dispersion of permethrin, a polymeric binder such as acrylic copolymer or polyvinylacetate, and optionally a cross-linking agent (e.g., methylated melamine resin), are used. In the single-side surface coating embodiment, the fabric is treated with the insecticide and a thickener (e.g., carboxymethylcellulose), and optionally a polymeric binder that is optionally cross-linked. ” Insecticidally treated fabric having improved wash durability and insecticidal efficacy and method for its production, Dixon et al 2004
The industrial permethrin is 250g/liter, and Sawyers Permethrin is 0.5%. 1% is 10g/liter, So I need to dilute a lot!
Military uniforms are treated with a higher concentration of permethrin. The amount of time and washings garments will remain an effective mosquito deterrent, increase with a higher concentration.
So I chose to use 2.5% solution. 250g/liter * volume = 25 grams = amount I'll pour into 1 liter of water. That's 100 ml of industrial permethrin per 1 liter of water.
I would only use a spray applicator for a backpack. I immerse clothes in the permethrin solution using rubber gloves for protection. For thick and heavy clothing, like jeans, I use a bucket. For thinner clothing I use a zip lock bag.
I massage the clothes in solution to make sure there is full penetration. You can soak clothes that are already damp, as in just out of the spin cycle of a machine washer. For a dry pair of jeans, you need about 750ml of solution (4 jeans per 3 liters).
After soaking I wring out the excess back into the bucket and hang dry. I soak, wring, and hang the next article of clothing, and by then I need to milk the previous as they have begun to drip.
The sun disintegrates permethrin, so hanging dry with an outdoor roof is best.
Depending on your climate, drying may take a long time. If jeans are still damp but no longer dripping (after 12 hours for me), I place them in the dryer. As a bonus, any untreated clothes placed in the dryer with the jeans will get a bit of permethrin as well.
If you want to be able to see through the mosquito net, make sure to choose a dark net. White nets reflect light and distort your visibility.