DEET is one of the most effective and common flea, tick, and mosquito repellents in the world. The active ingredient in about 120 commercially available products, it is considered safe for humans and the environment by the World Health Organization (WHO), the Environmental Protection Agency (EPA), and the Centers for Disease Control and Prevention (CDC). Despite its robust credentials, many people retain a strong buzz of concern about DEET.

How Does DEET Work?

A commonly cited 2019 study from researchers at Johns Hopkins University and Virginia Polytechnic Institute suggests that DEET changes the scent of human sweat and either makes humans smell noxious to mosquitoes or makes people harder for them to find. However, not enough is known about how mosquitoes process odors to understand precisely how the chemical repels them.

The National Pesticide Information Center says that about 30% of Americans use some formulation of DEET. They find it in various brand-name products at concentrations varying from 4% to 100%. The concentration percentage forecasts not how well a product will work but how long its effect will last.

By warding off mosquitoes and ticks that carry potentially deadly diseases like malaria, Zika, yellow fever, dengue fever, West Nile virus, Rocky Mountain spotted fever, and various forms of encephalitis, DEET has probably saved many millions of lives since the Army began using it in 1946 and the general public started in 1957.

Is DEET Bad for the Environment?

Not to be confused with DDT (a bug killer so toxic that its use in the United States was banned in 1972), DEET repels fleas, mosquitoes, and ticks. Its chemical name is N,N-diethyl-meta-toluamide.

DEET Pros and Cons

Pros:

The EPA stopped requiring manufacturer studies of DEET’s environmental safety by 1998 because it found early research compelling enough. Newer information about DEET is therefore sparse. Even so, governmental agencies and the scientific and medical communities around the world continue to consider DEET the gold standard among repellents.

That being said, DEET can melt sunglasses and speedos right off your body. (It does not like plastics, and the feeling is apparently mutual.) Fortunately, DEET does not appear to attack air, soil, and water as memorably as it does plastic and synthetics. 

How Does the Environment Rid Itself of DEET?

Many DEET products are sprays, so a fair amount of the chemical can end up in the air. Fortunately, sunlight de-composes it. In soil, bacteria and fungi break it down.

DEET doesn’t dissolve easily in water, and so is often found in streams and wastewater in high concentrations. However, this may not be as scary as it sounds.

A 2011 article in the peer-reviewed journal Integrated Environmental Assessment and Management showed DEET persisting in groundwater only at what are probably very safe levels. The concentration found was several hundred thousand times lower than that necessary to cause any observable effects in aquatic daphnids and green algae. Meanwhile, when DEET washes off human bodies into pool water, wet swimsuits stay intact. You can credit both sunlight and chlorine for that.

Biopesticides and Other Repellents

Biopesticides

According to Consumer Reports testing, essential oil of lemon eucalyptus (OLE) at a 30% concentration is as effective as DEET in repelling mosquitoes and ticks for up to 7 hours.

OLE is an oil extracted from the Australian lemon-scented gum eucalyptus tree. The active ingredient in the oil is the biopesticide para-Menthane-3,8-diom (PMD). Confusingly enough, OLE is not the same thing as lemon eucalyptus oil, which is distilled from the bark and leaves of the lemon eucalyptus tree and relies on the less effective citronella for its bug repellent properties.  

Products that contain OLE include Repel Eucalyptus Insect Repellent, Natrapel Lemon Eucalyptus Insect Repellent, and Off Botanicals.

IR3535 is a non-toxic synthetic repellant that the CDC classifies as a “biopesticide” because it is structurally like an amino acid that’s found in some wild plants. The EPA expects (but has not demonstrated) that it is environmentally safe. Consumer Reports found IR3535 to be less effective as a repellent than DEET, Picaridin (see below), or OLE. Products including Skin So Soft Bug Guard Plus Expedition and SkinSmart contain IR3535. 

As for other common repellent substances, Consumer Reports has assessed the essential oils of cedar, citronella, clove, lemongrass, peppermint, and rosemary for their use as mosquito and tick repellents. The tests showed that they aren’t “very effective, often failing in our tests within half an hour.”

Quasi-Natural Pesticides

Picaridin is a synthetic derivative of a compound found in peppercorn classified as a “conventional” repellent by the CDC. Consumer Reports found Picaridin to be roughly as effective as DEET, and the CDC recommends its use. Even though it’s man-made, Picaridin does not damage plastics and other synthetics. Examining records provided by the manufacturer, the EPA has found no risks to terrestrial and aquatic animals and plants from Picaridin.

Products including Cutter Advanced, Skin So Soft Bug Guard Plus, and Sawyer Premium Insect Repellent contain Picaridin.

2-undecanone is an organic compound that can be produced synthetically. However, its environmental effects have not been as thoroughly tested as those of other repellents. Products including Nonatz Bug Repellent contain 2-undecanone.

How to Apply DEET

While DEET sometimes comes in combination repellent/sunscreen products, it shouldn’t be slathered on like sunscreen. Neither should it be re-applied as regularly as sunscreen. Overuse can create toxic side effects. The CDC and EPA recommend that you:

  • Apply DEET when outdoors.
  • Avoid inhaling the spray.
  • Wash DEET off after returning indoors.
  • Wash any treated clothes.
  • Don’t apply DEET over cuts, wounds, or irritated skin.
  • Keep DEET away from eyes and mouth.
  • Use only enough to cover the area to be protected.
  • Keep the bottle out of reach of children.
  • Don’t use DEET on children younger than two months.
  • For applying to the skin of a child, spray DEET on an adult’s hands and then rub the hands on the skin that needs protection.
  • Use separate DEET and sunscreen products.