The Down and Dirty on DEET

By Brian Irwin

At six A.M this morning I awoke to the shrill of my son Andys frustrated voice. He was clawing at the bottom of the foot. The previous evening he and I were playing lacrosse when black flies and a few mosquitoes ran us inside. Theyd gotten to the soles of his feet, his first foot itch. He was miserable. A retracted ballpoint pen, hairbrush and a few swabs of After Bite later, he had stabilized. As his crying tapered off, his sniffly voice uttered bad bugs and Those bugs gave me a bug itch...I must have been tasty.Bites are uncomfortable, but they potentially carry more illness than itch. Conditions like West Nile Virus, Eastern Equine Encephalitis and Ehrlichiosis are not common, but are reported in the Northeast each summer, some cases in our immediate area. Other diseases like Lyme Disease are reported much more frequently. These conditions, including Lyme, are preventable in many cases, with the diligent use of an effective insect repellent. One such agent has been proven far more efficacious than others: N, N-diethyl-m-toluamide, or DEET.DEET has a nasty reputation as a potentially dangerous compound. It has been implicated in the development of seizures, coma and even death. Despite widespread concern, these complications are limited to studies based on the ingestion of DEET, not the application of the compound to a persons skin. So if you dont chug it, is DEET safe?The complications that may accompany DEET exposure are directly caused by the amount of the product that ends up in a persons systemic circulation. Although ingestion of DEET can lead to high blood levels, skin application leads to blood levels of many hundred times less. Although not impossible, itd be very difficult to expose enough skin to DEET such that blood levels climb into the dangerous range. Considering this, there are two major factors that determine how much DEET is absorbed.First, the higher concentration of DEET, the more potential absorption occurs. Higher concentrations of DEET actually are no more effective at insect repellency than lower concentrations, they simply last longer. For instance 5 percent DEET will provide 90 minutes of efficacy whereas 20 percent DEET will last around four hours. At 50 percent, the efficacy and longevity of DEET plateaus, so limiting your DEET concentration to 50 percent may be prudent.Second, consider the surface area covered. If you put DEET only on your neck and ears, very little of your surface area will be absorbing the chemical. If you coat your trunk and entire body, you may stand to absorb more. However, keep in mind that even in these cases; its extremely unlikely youll be absorbing a dangerous amount of DEET.What about kids? A Canadian review of literature (mostly American studies) found only 10 reports of seizures after dermal application in over 50 years of studies. Additionally, no reported cases were found after 1992. Considering an estimated 29 percent of our children are exposed to DEET, and that seizures occur in roughly 3 percent of all children regardless of cause, these 10 cases were likely coincidental. In addition, in a review of over 20,000 people accidentally exposed to DEET, the side effects (many of which were rashes) in children were overall, less severe than in adults. The American Academy of Pediatrics, a fairly conservative academy, even recommends the use of up to 30 percent DEET in children over two months of age.What about other repellent options? It would be nice to admit that other products are as effective as DEET, but safer, however this isnt true. Most other products have a short period of efficacy, and during that period are inferior to DEET. Natural alternatives, like oil of lemon eucalyptus may work, but actually may be more dangerous (in fact the EPA advises this product be avoided in children less than three years of age!). Citronella has actually been shown to be very effective against mosquitoes, however to maintain this efficacy it must be reapplied every 30 to 60 minutes.What is a person (or parent) to do? First, weigh the risks and benefits of DEET versus the critters. Skin applied DEET-induced health problems are something Ive never seen as a physician, nor do I know of a physician who has. Lyme Disease is something Ive seen many times. There were a few cases of EEE and West Nile virus cases in New Hampshire last year. There were no cases of DEET complications. Could DEET cause health problems? Yes. Is it likely that youd ever absorb enough to cause them? No. Are you more likely to get Lyme or to have a seizure from DEET. Definitely Lyme. After a Mothers Day hike my family extracted a total of 10 ticks from our familys skin. If you want the most chemical-free repellent option, netting or long sleeves are your best bet. But these buggers are good, and they find their way in. To DEET or not-DEET is a hard question. Its not definitely harmless stuff, but if you use it in the outdoors the odds of avoiding illness are definitely in your favor.