By Ron Liskey | July 27, 2017
Many respond to fears about West Nile Virus (WNV) and the normal annoyance of mosquito bites by slathering on the insect repellent, especially on their children. The most common choice is a DEET-based repellent.
A study released in 2003 showed certain DEET-based products to be the most effective, in that they lasted longer than other products. But DEET-based repellents aren’t just hazardous to mosquitoes. From a human health point of view, choosing a botanical-based repellent can make more sense.
How DEET works
DEET does not block the insects’ recognition of attracting odor signals or cause an active avoidance behavior in mosquitoes and fruit flies. Actually, DEET is an effective repellent because it disrupts the insects’ odorant receptors, which detect special odor signals the insect uses to locate a potential host or food source. DEET corrupts messages from attractive scents, and as a consequence mosquitoes and fruit flies lose their orientation.
The Hazards of DEET
DEET is a registered pesticide. DEET is short for N,N-diethyl-m-toluamide (also known as N,N-diethyl-3-methylbenzamide). It is a member of the toluene chemical family. Toluene is an organic solvent used in rubber and plastic cements and paint removers.
DEET is absorbed through the skin and passes into the blood. The Medical Sciences Bulletin, published by Pharmaceutical Information Associates Ltd. reports, “Up to 56% of DEET applied topically penetrates intact human skin and 17% is absorbed into the bloodstream.”
Blood concentrations of about 3 mg per liter have been reported several hours after DEET repellent was applied to skin in the prescribed fashion. DEET is also absorbed by the gut.
The most serious concerns about DEET are its effects on the central nervous system. Dr. Mohammed Abou-Donia of Duke University studied lab animals’ performance of neuro-behavioral tasks requiring muscle coordination. He found that lab animals exposed to the equivalent of average human doses of DEET performed far worse than untreated animals. Abou-Donia also found that combined exposure to DEET and permethrin, a mosquito spray ingredient, can lead to motor deficits and learning and memory dysfunction.
An emergency medicine bulletin notes that DEET may have significantly greater toxicity when combined with ethyl and isopropyl alcohols and freon which are components of some DEET repellents. In 1998, the US EPA made it illegal for any product containing DEET to make any child safety claims.
Products with DEET are required to carry the following instructions (often in very small type):
DEET should not be used at all for children under 6 months.
For children 6 months to 2 years, only concentrations of less than 10% DEET should be used, and only once a day.
For children 2-12 years old, only concentrations under 10% should be used, and repellents should not be applied more than 3 times a day.
For adults, Health Canada has banned products with DEET concentrations over 30%, citing health risks and evidence that increasing the percentage does not do much more to repel insects.
Health Canada has also banned two-in-one products which combine sunscreen and DEET, saying they create the potential for people be exposed to too much DEET.
Products containing DEET are now required to carry labels which specify:
- Do not apply over cuts, wounds, or irritated skin.
- Do not apply to hands or near eyes and mouth of young children.
- Do not allow young children to apply this product.
- After returning indoors, wash treated skin with soap and water.
- Do not use under clothing.
- Do not spray in enclosed areas.
Recommendations and precautions
Following these precautions reduces the risk, but does not eliminate it.
When using DEET, its best to wear long sleeves and long pants, and apply repellent to clothing rather than skin.
DEET-based products should only be applied sparingly; saturation does not increase efficiency.
DEET repellents should never be inhaled.
There are a number of effective, less toxic insect repellents available. They need to be applied more frequently than DEET-based repellents, but they do not carry the same health risks.
Two botanical repellents which performed particularly well in a Florida study were Repel Lemon Eucalyptus Lotion Insect Repellent (also marketed as FiteBite Plant Based Insect Repellent), which protected for 120 minutes, and Bite Blocker for Kids, a 2% soybean oil formula, which was effective for 95 minutes. Citronella products in the study provided about 30-40 minutes of protection.
In 2005, the U.S. Centers for Disease Control (CDC) granted approval to two healthier alternatives to DEET—picaridin and oil of lemon eucalyptus—for protection from mosquitoes.
Picaridin, long used to repel mosquitoes in other parts of the world, is finally available in the U.S. under the Cutter Advanced brand name.
Oil of lemon eucalyptus, which is derived from eucalyptus leaves and is the only plant-based active ingredient for insect repellents approved by the CDC, is available in several different forms, including Repel Lemon Eucalyptus, OFF! Botanicals, and Fight Bite Plant-Based Insect Repellent.
Some other good choices, according to the nonprofit National Coalition against the Misuse of Pesticides, include products containing geraniol (MosquitoGuard or Bite Stop), citronella (Natrapel), herbal extracts (Beat It Bug Buster) or essential oils (All Terrain).
The group also gives high marks to oil of lemon eucalyptus, such as that found in Repel’s Lemon Eucalyptus Insect Repellent.
Another leading nonprofit, Pesticide Action Network North America (PANNA), likes Herbal Armor, Buzz Away and Green Ban, each containing citronella and peppermint as well as various essential oils (cedar wood, lemongrass, etc.).
PANNA also lauds Bite Blocker, a blend of soybeans and coconut oils that provides four to eight hours of protection and, unlike many other brands, is safe to use on kids.
Bug shirts or hats are an excellent, non-toxic method of protection.
Outdoor mosquito control tips
Mosquito coil smoke contains about 70 different volatile organic compounds including allethrin, phenol, benzene, toluene and xylene, all quite toxic especially when burned and inhaled.
Using yellow outdoor light bulbs which do not attract insects can help reduce mosquito populations at night.
Another option is to use a fan when there is little wind since mosquitoes are not strong flyers.
Planting mosquito repelling plants like lemon balm, catnip, basil and lemon geraniums around outdoor sitting areas and encouraging mosquito predators like bats and dragonflies can help reduce mosquito populations.