Insect repellents represent one of the first lines of defense against attacks by blood feeding ticks and the diseases they can transmit. The most common products contain DEET and are applied to skin. An alternative personal-use repellent strategy is to apply repellent or toxicant products (usually permethrin) to clothing or other fabrics rather than directly on the skin. This method has many positive features, including that chemicals are not applied to skin, potentially reducing chemical exposure as well as increasing the duration of efficacy, which can last through multiple launderings.
During a two-day, indoor, controlled study we compared the number of tick bites on individuals wearing either permethrin-treated or untreated summer weight clothing (T-shirt, shorts, socks and sneakers). Colony-reared, pathogen-free nymphal blacklegged ticks were placed on the left shoe, right leg above the knee and left arm just above the elbow of 15 human volunteers wearing untreated (no repellent) outfits or outfits treated with permethrin either commercially (Insect Shield) or using a do-at-home treatment kit (Sawyer Products). At the end of the 2-hour test period the number and location of ticks attached to subjects' skin were recorded. On the following day the same volunteers were placed in different treatment groups, given new outfits and subjected to the same tick challenge and activity regimen as the previous day. Regardless of the permethrin application method, subjects wearing outfits treated with permethrin received 3.36 times (odds ratio=0.298 with a 95%CI (0.221,0.401)) fewer tick bites than subjects wearing outfits with no repellent. However, the success of permethrin- treated clothing to reduce tick bites varied depending on the specific treated article of clothing. Only 1 (0.5%) tick bite was received (on the leg related to where ticks were applied to the shoes) among all subjects wearing permethrin-treated sneakers and socks compared to a 27% (n=100) tick attachment rate on subjects wearing untreated sneakers and socks. Subjects wearing permethrin treated shorts and T-shirts were 5 and 2.2 times, respectively, less likely to receive a tick bite in areas related to those specific garments than subjects wearing untreated shorts and T-shirts. On the second day of the study only, ticks attached to subjects were classified as alive or dead prior to removal. From five subjects wearing untreated outfits, 97.6% (82 of 84) of attached nymphs were classified as alive while, significantly fewer (22.6%, 17 of 75) attached nymphs were alive on the 10 subjects wearing treated outfits.
These results confirm findings from studies demonstrating the effectiveness of permethrin-treated military weight clothing for protecting against tick bites, but importantly, extend the observation to summer weight clothing more likely to be worn by people during the summer when tick activity and the potential for tick-borne pathogen transmission is greatest.