5-22-2006 Is DEET Safe and Effective

Is DEET safe and effective?

Application of DEET has been recommended to prevent bites from insects/ticks that can cause West Nile Virus or Lyme disease. DEET (N,N-diethyl-m-toluamide) is the most effective of insect repellents. Non-DEET repellants do not demonstrate appropriate protection against insect bites. An estimated 29% of American children are exposed to DEET. The concern has been caused by case reports associating use in children with precipitation of seizures.

Mechanism of action is unknown but it is thought that the chemical disturbs the function of receptors in the mosquito's antennae that allow it to locate humans. Effectiveness and duration of action of repellant is directly related to concentration of chemical. Products are available in variable concentrations and in various forms: aerosols, pump sprays, lotions, creams, liquids, sticks, etc.

The concern about seizures is extrapolated from case reports of ingestion of the chemical. Hypotension, seizures, and coma have occurred within an hour of ingestion. The mechanism of seizures is unknown.

• Ten case reports describing seizures in children following application of DEET have been reported in the last 50 years and none have been published since 1992. Because seizure disorders occur in 3-5% of children and 29% of children are exposed to DEET, one could

see an association by chance. Epidemiologically, when two events are both prevalent, case reports are not good measures to use to determine causation. The evidence does not support an increased risk of adverse events or seizures in young children.

Safety of administration of DEET during pregnancy is supported in animal studies and in a randomized, double-blind trial involving 897 pregnant women in Thailand who continuously applied therapeutic doses of DEET topically during the second and third trimester vs. placebo. Cord blood samples demonstrated that the chemical crosses the placenta. There were no neurological, gastrointestinal, or dermatological effects in the women exposed to DEET. There were no adverse effects in the babies and growth and development were normal at one year of age. There are no studies of application during the first trimester.

Recommendations: *

Children 6 months to 2 years should be limited to one application per day Children 2-12 years should be limited to 3 applications per day

The maximum concentration used should be 10% or less for children up to 12 years of age.

•These low concentrations are effective for 2-3 hours. DEET will be washed away in water. A second application of DEET may be warranted if the child is out of doors for more than 12 hours.

•Limit time spent out of doors at dawn and dusk Wear protective clothing

*CMAJ 2003:169(3) 209-11

I am interested in any questions that you would like answered in "Question of the Week." Please e-mail me with any suggestions at donna.seger @vumc.org

Donna Seger, M.D.

Medical Director, Tennessee Poison Center

This question was first released on July 12, 2004