The Gnats are Bad! Safe Insect Repellents

The biting gnats of the south are annoying and painful. In coastal Georgia, there are about 25 species of gnats, or biting midges. Three of the 25ish species do most of the biting in the spring (March and April) and fall (August and September). Let’s review insect-repelling options and the possible health effects of a variety of insect-repelling options, from conventional chemical repellents like DEET and permethrin to natural alternatives such as essential oils and coconut-derived compounds.

A biting midge (gnat) engorged with blood. Image credit: E. Scmidtmann USDA

Permethrin

Pyrethrins are a class of pesticides derived from chrysanthemums and are not typically used on humans as insect repellents. Permethrin, a synthetic version of pyrethrins, is considered safe for topical use on humans. However, numerous studies suggest that exposure to both of these chemicals—whether through environmental contact or topical application—is associated with an increased risk of developing Parkinson’s disease and other chronic neurodegenerative conditions. In animal models, the development of these conditions is clearly dose-dependent and time-dependent, with earlier life exposure linked to a higher risk.1 In human studies, researchers primarily evaluate populations such as farmers who use pyrethrins in agricultural settings.

DEET

DEET (N,N-diethyl-meta-toluamide) has been the gold standard for insect repellents for over 50 years, despite its mechanism of action remaining somewhat unclear. It is believed to interfere with an insect’s ability to detect human odors—particularly L-lactic acid and carbon dioxide—which are key cues insects use to locate hosts. Insects "smell" via their antennae, which contain sensory receptors.

According to the National Pesticide Information Center (NPIC), DEET repels "flying insects such as biting flies, midges, black flies, chiggers, no-see-ums, fleas, mosquitoes, and ticks."2 The inclusion of ticks is particularly interesting, as they are arachnids, not insects, and do not have antennae. Instead, ticks detect hosts through a specialized sensory structure called the Haller’s organ.

The NPIC also reports that DEET is slightly toxic to birds, and although rare, neurological side effects in humans have been documented. These effects include encephalopathy, seizures, tremors, slurred speech, coma, and even death. Reported cases of toxicity have involved both ingestion and "improper dermal application," such as using DEET in ways not consistent with product labeling.2

When DEET is used in combination with sunscreens containing oxybenzone, both chemicals can enhance each other’s dermal absorption. This interaction has been observed in both animal models and human studies by measuring the urinary metabolites of each chemical. 3

To minimize risk, it is recommended to use sunscreens with zinc oxide and/or titanium dioxide as active ingredients—these are currently the only sunscreen ingredients recognized as safe and effective by the U.S. FDA.

Essential oils

Essential oil blends contain fragrant plant-derived oils that may help mask the human scent, making individuals less detectable to insects. Citronella oil, primarily extracted from Cymbopogon nardus, has demonstrated good efficacy against mosquitoes. Several other essential oils have also shown insect-repellent properties, including carrot seed oil, neem seed oil, Artemisia absinthium (wormwood), eucalyptus, catnip, and Carpesium abrotanoides (commonly known as pig’s head). However, not all essential oils are equally effective—lavender and geranium, for example, have shown poor repellent activity in studies.4

When using essential oils for insect repellent, proper dilution is essential to avoid skin irritation or toxicity. If you plan to make a blend, it’s a good idea to search PubMed or other scientific databases for studies linking specific essential oils with insect-repellent efficacy. Keep in mind that most studies focus on mosquitoes, not gnats or other pests, and the effectiveness of essential oils generally lasts only 2–4 hours after application.

Importantly, remember that just because a substance is plant-derived does not mean it is inherently safe. For example, pyrethrins, which are natural insecticides extracted from chrysanthemums, have been associated with an increased risk of neurodegenerative diseases such as Parkinson’s.

Coconut oil

Coconut oil contains medium-chain fatty acids (MCFAs), some of which have been shown to possess insect-repellent properties. In studies involving cattle, certain fatty acids derived from coconut oil were found to repel biting flies and bedbugs for up to two weeks and ticks for up to one week after application.5 Additionally, these compounds have demonstrated repellent effects against mosquitoes.5

However, it’s important to note that coconut oil itself is not the same as the isolated fatty acids it contains. On its own, coconut oil has not been shown to repel insects effectively. That said, applying coconut oil—or any oil—to the skin can make it difficult for gnats and other small insects to land and bite, as the oil creates a slick surface where some may get trapped and die.

References:

1. Nasuti C, Brunori G, Eusepi P, Marinelli L, Ciccocioppo R, Gabbianelli R. Early life exposure to permethrin: a progressive animal model of Parkinson's disease. J Pharmacol Toxicol Methods. 2017 Jan-Feb;83:80-86. doi: 10.1016/j.vascn.2016.10.003. Epub 2016 Oct 15. PMID: 27756609.

2. https://npic.orst.edu/factsheets/archive/DEETtech.html

3. Yang Y, Guo L, Li S, Zhang P. Association between percutaneous absorption of benzophenone-3 and N, N-diethyl-m-toluamide among the general adult population. Sci Total Environ. 2024 Nov 15;951:175360. doi: 10.1016/j.scitotenv.2024.175360. Epub 2024 Aug 8. PMID: 39122035.

4. Jaenson TG, Garboui S, Palsson K. Repellency of oils of lemon eucalyptus, geranium, and lavender and the mosquito repellent MyggA natural to Ixodes ricinus (Acari: Ixodidae) in the laboratory and field. J Med Entomol. 2006 Jul;43(4):731-6. doi: 10.1603/0022-2585(2006)43[731:rooole]2.0.co;2. PMID: 16892632.

5. Zhu JJ, Cermak SC, Kenar JA, Brewer G, Haynes KF, Boxler D, Baker PD, Wang D, Wang C, Li AY, Xue RD, Shen Y, Wang F, Agramonte NM, Bernier UR, de Oliveira Filho JG, Borges LMF, Friesen K, Taylor DB. Better than DEET Repellent Compounds Derived from Coconut Oil. Sci Rep. 2018 Sep 19;8(1):14053. doi: 10.1038/s41598-018-32373-7. PMID: 30232355; PMCID: PMC6145915.