Summer is slowly starting to roll around. The days are longer, the air is warmer, kids are out of school, the beaches are filling up, and the mosquitos —those pesky little buggers with painful bites, who carry diseases—are everywhere! In the US we are potentially susceptible to mosquito-borne viruses like West Nile and Zika (though Zika is rare in the US, it has had significant media coverage recently), and La Crosse Encephalitis, to name a few. With those inconvenient and potentially diseased insects in mind, bug spray is a staple of summer in most homes. The most common active ingredient in insect repellants is, hands down, a substance called N, N-diethyltoluamide, or C12H17NO. Doesn’t ring a bell? That’s okay. Odds are you’re in good company. That fancy chemical compound is more commonly known as DEET, and it is seriously effective stuff! This pesticide was originally developed for the US Army in the 1940’s to protect soldiers from insect-infested, jungle battlefields. But in recent years, questions have been raised about it’s safety. Some individuals claim that it’s highly toxic and will destroy your brain and nervous system, while others argue that it’s perfectly safe, and that those who affirm its toxicity are uninformed and are spouting hippie propaganda. As is often the case, these are two drastically differing viewpoints and those who hold them are both deeply invested in their opinion. And, as always, we will delve into this disagreement using our sharpest weapon and most reliable tool—science!
The primary way we encounter DEET is topically, as we spritz bug spray on every bit of exposed skin before we head out into the woods, or sit down for a picnic. The Environmental Protection Agency (EPA) reports that DEET continues, time-after-time, to test as safe and as having no negative health risks or effects associated with it.
This is interesting, as since the 1980’s, National Park employees have been reporting a variety of negative effects of DEET exposure, including rashes, redness, burning, and numbness at the sites of application, as well as the lining of the nose, mouth, and lips (transferred from hands). The National Pesticide Information Center (NPIC) confirms this, adding that irritation is more likely if the area of application is where skin rubs against itself (such as backs of knees, thighs, inner elbows) or under clothes. As far back as the 1970’s, scientists such as Miabach and Johnson have been recording urticaria, or dermatitis, in adults and children after the topical application of DEET. In fact, in 1982 an isolated case was documented wherein limited exposure lead not only to dermatitis, but also anaphylaxis! The US Army did some studies of their own, testing 75% DEET on the upper arms and creases of the elbows of 77 volunteers. Forty-eight percent of the participants developed severe reactions in the elbow.
It is not uncommon for DEET to end up inside your body, too. Once it has come in contact with your hands, as pointed out in the earlier mention of the National Park employees, it is easily transferred to the mouth, eyes, and nose. Additionally, since most exposure is from sprays, inhalation of small amounts is almost inevitable. DEET, like most other substances, is also absorbed through the skin into the bloodstream. In fact, it can continue to be absorbed for up to 12 hours after application.
The good news is this: once DEET has been internalized, it only stays in your system for about 24 hours, gets filtered out by the liver, and expelled through urine. There is much concern voiced by those worried about DEET that internal exposure can lead to cancer, or pregnancy complications/birth defects if exposed while with child. But there are no studies available that show any such link.
Another concern about DEET is that it is neurotoxic—that is to say, it can cause damage or dysfunction to the nervous system. Dr. Abou-Donia of Duke University studied the effects of DEET on lab animal’s coordination, and ability to perform tasks. I’ll spare you the fascinating science (okay, most people might not find it so fascinating), and skip to his conclusion: animals that were exposed to amounts of DEET comparable to a standard human dose experienced much more notable memory impairment and cognitive dysfunction than his control group, or the critters who were not exposed to any DEET.
French scientists at the University of Angers and the Institute of Research and Development in Montpellier state that more research is needed into the effects on humans, however they have been doing extensive cellular research on mice. These clever men and women found something very interesting—that DEET blocks a certain enzyme that controls neurotransmitters, the body's chemical messenger system. They conclude that the safety of DEET for human use is... questionable. But bear in mind, these tests were done on rodents and/or individual cells in test tubes, so some other experts question how directly these findings can be translated to a human model.
In 1986, Everglades National Park employees who had extensive DEET exposure participated in a formal questionnaire. The results showed that these individuals who had great and chronic contact were far more likely to experience insomnia, cognitive dysfunction, and mood swings than their colleagues who had lesser exposure. There is also an isolated report of a man who applied DEET topically, then later in the day enjoyed a long steam in a sauna, then presented with sudden mania, psychosis, hyperactivity, aggression, and delusions. While extremely disconcerting, it is important to remember that this is the only reported case with a definitive connection. Although, I would never recommend spending time in a sauna after the application of DEET, just to be safe.
Fortunately there are some effective natural insect repellant options, such as sprays containing essential oils like lemon, rosemary, peppermint, eucalyptus, tea tree, cedarwood, lavender, and lemongrass. Citronella, lemongrass, and rosemary, on their own, have not been proven to be significantly useful in deterring insect bites, but when blended together with other oils, and suspended in a base such as witch hazel, it is this author's observation that they seem to be at least equally effective as DEET-based products, if not more so, in North American climates ranging from northern New England to the Deep South. Natural sprays tend to require more frequent application, but they typically smell very appealing and don’t leave your skin feeling sticky.
So, the verdict. As with many issues, it’s not a clear-cut answer. There are many significant studies showing DEET’s negative dermatological effects, and some studies suggesting some pretty serious neurological implications, especially for children, those with other medical conditions, and when experiencing prolonged or chronic exposure. But there are also some studies with opposing views that strongly support the safety of DEET in humans. In my personal and professional opinion, and as someone with preexisting neurological issues, DEET is at least a moderate concern, and for standard activity, such as gardening, picnics, or spending the day on the lake, I don’t feel there is a need to resort to the use of DEET. However, if you’re heading into the depths of the jungle where blood-sucking insects are a dime a dozen and frequently carry deadly diseases, a DEET-based repellent is something worth strongly considering.
These facts and opinions are those of a certified Master Herbalist and Dipl. Natural Health Consultant, and Reiki Master Teacher, and are for educational purposes only, and not intended to replace consult with your qualified healthcare practitioner.