The Details & Dangers of DEET

Author: Mosquito Squad of Greater Saint Louis

Whenever I apply insect repellent containing DEET I feel guilty that I am doing evil unto my body.  I worry about vague notions of cancer and neurological damage that I casually heard from the media or my grandmother.  Finally, after all these years, I sat down and researched DEET.  This is what I found:


DEET was first used by the US Military in 1946 in mosquito-infested war zones and later approved for civilian use in 1957.

How it Works

From what I gather, the jury is still out on precisely how DEET works.  For about fifty years, scientists generally agreed that the chemical interfered with the mosquito’s olfactory system, meaning DEET blocked its sense of smell and thus it could not sense human sweat or breath when it was exposed to DEET.  However, a study conducted in 2008 demonstrated that DEET actually functions as a true repellent rather than a chemical that blocks the mosquito’s olfactory sensors.  In the study, the mosquitoes were repelled from the target that contained no traces of human or carbon dioxide.  In September 21, 2011 research published new results that showed that mosquitoes can still smell humans who are wearing DEET, but that they become confused.  So as I said, scientists don’t know exactly how DEET works, but it works.

One thing scientists do know is that the higher the concentration of DEET, the longer the period of time during which one application will repel bugs. 

*Use a higher concentration product (20% or higher) for protection from ticks.

*Use higher concentrations for longer periods of protection between applications and in situations where populations of biting insects are high.

Health Effects

After passing through the DEET website, the latest Environmental Protection Agency (EPA) DEET chemical reregistration document, and the Center for Disease Control’s (CDC) page about DEET, I have discovered that using DEET is considered the lesser of two evils.  DEET has been shown to be completely safe for humans when used properly.  The EPA and CDC think that the protection from dangerous diseases, i.e. West Nile virus and Lyme disease, outweighs the potential risk of inhaling or ingesting small amounts of DEET.  DEET is recommended for pregnant women as a way to safeguard against contracting West Nile virus and is approved for use in children when the concentration is 30% or less.  DEET is not recommended for use on infants younger than 2 months.

Some side effects that can result from DEET include skin rashes, blisters, and irritation of the skin mucous membrane.  In several rare cases, the overdose and/or misuse of DEET on children resulted in brain effects (encephalophathy) and seizures.

How to Use DEET Safely

Some basic rules from the CDC regarding safe DEET use:

1. Use DEET sparingly.

2. Use DEET only on intact skin (not cut/wounded) and on exposed areas (not underneath clothing).

3. Wash skin with soap and water when you return indoors.

4. Check the label for DEET concentration.  If it is a low concentration it may be necessary to reapply later.

Some more Do’s and Don’ts from the CDC:


-Read and follow all directions and precautions on the product label.

-Store DEET out of reach of children.

-Avoid applying repellent to infants less than 2 months old.

-Avoid over-application of this product.

-Use just enough repellent to cover exposed skin and/or clothing.

-Wash treated skin with soap and water after returning indoors.

-Wash treated clothing before wearing it again.

-Spray on hands and rub on the face to apply to face.


-Spray directly onto face.

-Apply over cuts, wounds, or irritated skin.

-Apply to hands or near eyes and mouth of young children.

-Allow young children to apply this product.

-Spray aerosol or pump products in enclosed areas.

-Use on children’s bedding or bedclothes.

DEET and the Sun

An important note: because of its chemical makeup, DEET diminishes the effectiveness of sunscreen.  Furthermore, the EPA no longer allows companies to combine sunscreen ingredients with DEET in a single product because sunscreen should be applied liberally, whereas DEET should always be used sparingly.  Therefore if you are in a sunny, bug-infested area you should apply sunscreen first, let it soak in, and then apply DEET.  Continue to reapply sunscreen frequently, but only reapply DEET once the bugs start biting again.

Is DEET Safe to Spray on Pets?

Do not use DEET on pets because if they lick their paws they will ingest the chemical, which is toxic when ingested.   You are better off buying a special insect repellent from your vet, getting the animal vaccinated, or using a barrier spray on your property.

Does DEET Cause Cancer?

No, the EPA has classified DEET as non-carcinogenic.

Will DEET Harm Clothing?

DEET does not affect cotton, nylon or other fabrics, however, it may damage rayon, leather, and plastics.