Deet repellents work by evaporation, creating a shield a few inches above the area of application. The presence of the repellent vapor confuses insects so they can’t locate a target host. In most cases, it usually requires less than 1% of the repellent to form this protective barrier. It is the combination of this “evaporation delivery system”, and the base repellent you choose that determines how much repellent you must apply. Different technologies used in making repellents will determine the initial application and re-application required for basic protection. Another consideration must also include the insect you’re trying to repel. While most mosquitoes in the U.S. respond to basic application levels, some more aggressive species found in Africa will require a more frequent application. Until recent outbreaks of West Nile encephalitis and an infrequent instance of malaria on the U.S. east coast, mosquito bites were considered nuisances with little regard to disease issues.
Essential Oils: Many compounds that occur in nature provide a brief period of repellency against certain insects. There are well over 150 natural repellents while the most common are: Citronella, Eucalyptus, Lemon Leaves, Peppermint, Lavender, Cedar Oil, Canola, Rosemary, Pennyroyal, and Cajeput. Persons concerned about exposure to deet or who prefer a natural solution can use essential oils. Generally, the EPA considers these oils safe to use in low dosage but overall their effectiveness is limited to less than 30 minutes.
Deet (N,N-diethyl-m-toluamide): Deet is by far the most commonly used insect repellent worldwide. This is because it is the most effective repellent against mosquitoes, ticks and other biting insects. After researching hundreds of compounds, deet was selected by the USDA and the US Military as the safest and most economical. See comments regarding use on children available at American Academy of Pediatrics
R-326 (Di-n-propyl Isocinchomeronate): R-326 is the most effective insect repellent against flies, gnats, no-see-ums, and similar pesky insects. R-326 is far more effective than deet against these insects and R-326 only needs to be present in small quantities.
MGK-264 (N-octyl bicycloheptene dicarboximide): MGK 264 is both a mosquito repellent and a synergist. As a synergist, MGK 264 both repels mosquitoes and helps the deet to do an even better job of repelling mosquitoes than it would by itself. The MGK 264 molecule is much larger than the deet molecule in size and thus not absorbed well by the skin.
Permethrin: Although known as a repellent, permethrin is actually a contact insecticide. That is, it kills ticks or other insects that come in contact with it. Permethrin is considered ideal because it is applied to clothing, gear, mosquito nets and bedding and is not applied directly to the body. When applied to clothing and equipment, permethrin is very effective at reducing the mosquito population in your campsite or sleeping quarters by killing mosquitoes that “hang around” camp and land on things. Where ticks are a concern, permethrin on clothing or gear will kill ticks that travel across as little as 10″ of treated fabric. Spray applications of permethrin remain effective up several weeks and through weekly washings. Dip applications can remain effective even longer. Permethrin using different carriers are harmless to skin and is used extensively in other formulas for treatment of head lice and other conditions but let’s emphasize again – products sold for protection from tick and mosquito are only to be applied to clothing and gear.
Read more about permethrin
Delivery Systems: Whether you choose deet or essential oils, the delivery system is through evaporation. If you choose permethrin, the delivery system is through treatment of clothing or gear.
Deet is used in numerous formulations that combine it at different strengths and with carriers such as alcohol, polymers or others. Deet is also blended with other repellents noted earlier . . . the options are numerous. Deet has been found to limit incremental protection when concentrations go beyond 35%. Most formulations of deet are now water-based.
Controlled Release: (Sub-Micron Encapsulation): Introduced in 1998, is by far the most advanced and effective delivery system available. The active ingredient, deet, is encapsulated (surrounded) at a 20% concentration within a skin nourishing protein just the way air is captured within a ping pong ball . . . and the system is water based. An application of Controlled Release contains many of these protein ping-pong balls that are suspended in a water-based lotion. After contact with skin, the protein balls begin to break down releasing the captured deet. The process continues as each microscopic ball is depleted then replaced by a new ball that contacts the skin, releases its deet and so on. The process takes up to 24 hours for one application. The initial application can be adjusted when the user is in an area of more aggressive insects. To adjust simply apply more product during initial application, with no need to reapply during the day. The only commercially available product using this technology is Sawyer Controlled Release
Because protein’s adherence to the skin is so effective, these formulas are very resistant to perspiration (sweat-off), and water. When applied they are dry and comfortable with no greasiness. This system results in very effective protection and is the safest repellent by far. However, it is only effective when used on skin because clothing does not have the capability to release the proteins.
Entrapment: This system uses a polymer to encase the repellent (deet), which slows down the early evaporation leaving more deet available for later evaporation. This system can often increase a repellent’s length of effectiveness by 25% to 50% over comparable non-entrapped deet products. The negatives of this system are that these formulas are often greasy because of the presence of the polymer. The only commercially available product using this technology is 3M Ultrathon
Lotions: The active ingredients in a repellent formula suspended in a lotion can be gentler to the skin, and up to 50% more effective than comparable sprays.
Sprays: For convenience, most repellents are applied in a spray format. Sprays usually use an alcohol base to carry and disperse the deet; however, alcohol promotes premature evaporation and in turn shortens the effective period of the protection. Alcohol can also open skin pores and promote deet absorption. Water-based and low percentage alcohol formulas are better. These formulas work best on clothing but are only effective on skin for short periods. Non-Controlled Release formulas should be avoided if frequent re-applications are required such as for use on camping trips, or any time potential deet absorption is a concern.
Recent adverse publicity has left many people confused and concerned about the safety of deet. Although deet does not create a skin sensitivity, it is a skin irritant. This means that after a period of frequent and repeated use, your skin may become red or even sore to the touch. While your skin will recover between uses, each subsequent use could again display irritation. The amount of deet that can be used prior to developing skin irritation varies from person to person. The term sensitivity refers to the condition in which skin develops a resistance to the presence of a chemical and an allergic-type reaction takes place if that chemical is present on the skin. Deet has been well studied and does not cause people to develop skin sensitivity, resistance, or allergic reaction to it. We recommend that your choice of deet products be kept below 35%.
Some segments of the medical community have recently expressed concern over the amount of deet absorbed by the skin, especially in children. To date, absorption studies relating to deet indicate that the body releases the deet it absorbs. It is not something which can be defined exactly. However, literally billions of applications of deet occur annually, and deet has been in widespread use since 1954. There are no studies or clinical observations to suggest long-term dangers of deet when used properly and in accordance with label directions. With the new water-based (versus traditional alcohol-based) Sub Micron Encapsulation techniques used in Sawyer Controlled Release formulas, the traditional concerns about exposure to deet are alleviated.
KNOWN ABSORPTION STUDIES OF DEET
To date, only two studies have been conducted regarding the skin absorption rate of deet:
The first was a series of studies conducted by the industry in Belgium in the mid-1980’s. In all, eight human subjects were observed. It is from these studies that the generally accepted 4% to 8% absorption rate, which is often used by the medical community, was obtained. Due to the complexity of the study, not all deet applied could be accounted for, but based on a long history of animal studies conducted by manufacturers during the EPA approval process, it was concluded that none of the deet remains in the human body after 72 hours.
The second study was conducted in California in 1995 where deet was observed as part of a blend with R-11, a repellent similar to R-326, and MGK-264. In this study four human subjects were observed. The conclusion of the study was that when combined with these two larger molecules, the absorption rate of deet was reduced to a range of 3% to 6%. This represented a reduction in absorption of 25%. This blend is used in the Sawyer composites.
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