Permethrin is an insecticide that is commonly used to help repel and kill ticks, mosquitoes, and other insects. It can be applied to clothing, tents, sleeping bags, and other fabrics. A frequent question is whether clothes need to be washed after being sprayed with permethrin. Here is a look at the key considerations.
How Permethrin Works
Permethrin is a synthetic insecticide that works as a contact insecticide, repellent, and insect growth regulator. It is effective against a broad range of insects including mosquitoes, ticks, fleas, and flies.
When sprayed on fabrics, permethrin binds very tightly to the fabric fibers through hydrogen bonding. It does not absorb into the fabric, but rather forms a protective coating on the surface. This surface layer of permethrin is what repels and kills insects that come into contact with the treated fabric.
Washing Treated Clothes
Since permethrin binds so tightly to fabric fibers, it is resistant to being washed out through laundering. Numerous studies have shown that permethrin-treated clothing retains insecticidal effectiveness even after multiple washings.
For example, one study found that military uniforms still had significant tick-killing effectiveness after being washed 6 times in a washing machine. Other studies found mosquito repellency and knockdown activity even after 20 wash cycles.
While a very small amount of the permethrin may be lost during washing, the majority remains bound to the fibers, continuing to provide excellent insect repellency and knockdown after laundering.
How Many Washes Remove Permethrin?
Most research indicates that permethrin-treated clothing retains insecticidal effectiveness through at least 6 wash cycles when machine washed in detergent and water. Some studies have shown longer lasting activity of 10-20 washes.
The U.S. military has done extensive testing on permethrin-treated uniforms. They recommend the application of permethrin is effective for up to 50 washings when laundered according to the fabric’s washing instructions.
Should You Wash New Clothes Before Applying Permethrin?
Many people wonder if new clothes should be washed first before treating with permethrin. Since permethrin binds so tightly to fabric fibers, pre-washing is generally not necessary.
In fact, some research indicates that applying permethrin before washing helps it bind most effectively to fabrics. The initial application allows permethrin to form strong hydrophobic and hydrogen bonds before any washings could potentially disrupt a small percentage of those bonds.
Pros and Cons of Washing After Permethrin Treatment
| Pros | Cons |
|---|---|
| May reduce any initial odors from the permethrin spray | Will remove a very small fraction of the permethrin |
| Can wash away any initial residue/stickiness | Washing and drying takes extra time and energy |
| May brighten clothes if washed with bleach | No major benefits since permethrin is so wash-fast |
Precautions When Washing Permethrin-Treated Clothes
While washing permethrin-treated clothes is low risk, there are some simple precautions that can be taken:
- Wash only with other permethrin-treated items. Do not mix in untreated clothing.
- Use cold or warm water, not hot water.
- Use a full wash cycle length.
- Line dry or tumble dry on low if concerned about losing effectiveness.
Alternatives to Washing
Rather than washing clothes after permethrin treatment, some other options include:
- Letting clothes air out for a day or two to dissipate any odor or residue.
- Spraying down clothes lightly with clean water from a hose or sink to remove any stickiness.
- Storing clothes in a ventilated area such as hung outside or in a garage. The fresh air circulation helps dissipate odors.
Conclusion
The bottom line is that washing permethrin-treated clothes is unnecessary. Permethrin binds extremely tightly to fabric fibers and is highly resistant to being washed out. Studies have shown treated clothing retains insecticidal effectiveness even after many laundry cycles.
However, if you choose to wash treated clothes, using cold or warm water and washing with other permethrin items is recommended. Letting clothes air out or lightly rinsing are other options to consider instead of full washing. Enjoy the great insect protection permethrin offers without worrying about having to re-treat after washing.