JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
insecticides are not dependent on gaseous barriers and are synthetic chemicals designed to kill insects on contact.³,⁴
cases of presumed DEET neurotoxicity probably occurred by chance alone and were unrelated to DEET toxicity.⁸ In another study, Briassoulis et al. found 17 reports of DEET-induced encephalopathy in children. Of these, the most common exposures followed either accidental ingestions or repeated heavy dermal applications.¹⁰ The FDA recommends not applying DEET in children younger than two months of age. The American Academy of Pediatrics recommends that children be treated with maximum DEET formulation strengths of 30%.¹¹ In summary, several studies have demonstrated that DEET may have possible adverse CNS effects after ingestions and following excessive reapplications, especially in children; but these adverse effects are very rare and occur infrequently.
The U.S. Food and Drug Administration (FDA) tests and approves all topical insect repellents for human use; while the U.S. Environmental Protection Agency (EPA) tests and approves all insecticides for non-human applications. Table 1 compares the formulations, strengths (in percent), efficacies, safety, and adverse effects of the currently approved mosquito repellents and insecticides for human applications.⁵
DEET
In widespread use since its introduction in the 1950s, N, N-diethyl-3-methylbenzamide, formerly N, N-diethyl-m- toluamide (DEET), is the most frequently used topical insect repellent and is among the safest. DEET is oilier than picaridin and may damage plastics and some synthetic fabrics in clothing, but will not stain or damage cotton, wool, and nylon. Lupi and co-investigators compared 4% and 15% formulations of DEET and demonstrated that the lower strength formulations could prevent A. aegypti mosquito bites for 1-7.5 hours. In addition, the DEET formulations were even more effective against A. albopictus bites lasting 5-8 hours.³ With 25% DEET formulation applied to the hand, the attraction rates decreased to 7% for A. albopictus and 6% for A. aegypti .³
ADVERSE EFFECTS OF DEET IN PREGNANCY
Pregnant women with increased minute volumes of ventilation exhale more carbon dioxide and attract more mosquito bites than non-pregnant women and men. Therefore, pregnant women are physiologically predisposed tomosquito bites and to mosquito-transmitted Zika virus disease with fetal microcephaly and ocular abnormalities. McGready et al. found no adverse effects of DEET on pregnant patients or their newborns in a double-blind study on DEET safety during the second and third trimesters.¹⁰ In a 1994 animal study, researchers found that pregnant rats fed DEET doses higher than normal human topical doses (325 mg/kg daily) demonstrated maternal toxic effects and had low birth weight newborns.⁸ However, there were no fetal toxic effects or malformations observed in the newborns.⁸ The Environmental Working Group (EWG) advises pregnant women to only use DEET repellents with 20-30% concentrations.¹²
DEET AND SUNSCREENS
DEET-containing sunscreens penetrate the skin more rapidly than DEET alone, may cause neurotoxicity, and are not recommended for use, especially in children.⁶,⁷ In a 2004 study, Ross et al. applied both topical 20% DEET-only and 10% DEET with sunscreen formulations to mouse skin.⁶ The 10% DEET formulations with sunscreen penetrated mouse skin faster in five versus 30 minutes and to a 3.4-fold greater depth than the 20% DEET formulations without sunscreen.⁶ In addition, the combination product demonstrated an average of 33% reduction in sun protection factor (SPF) because the active ingredients of the repellent disrupted the protective layer provided by the sunscreen.⁶ Since sunscreens should be re- applied every few hours and after sweating, swimming, and towel-drying, topical insect repellents should typically be applied prior to sunscreens.⁶,⁷
PICARIDIN
Picaridin is the most recently introduced insect repellent and, after DEET, the second most effective repellent for Aedes species mosquitoes. Picaridin is an appropriate and effective alternative for DEET. Lupi and co-investigators found that picaridin provided protection for up to 1-6 hours against both A. aegypti and A. albopictus bites.³ Van Roey and coauthors compared different formulations of picaridin, 10% lotion and 20% spray, with 20% DEET formulations and demonstrated that the higher concentrations of picaridin repelled mosquitoes similarly to DEET.¹³
THE ADVERSE EFFECTS OF DEET IN CHILDREN
DEET is remarkably safe, with 43 case reports on DEET toxicity in the past five decades, 25 of whichpresentedwith central nervous system (CNS) involvement, one with cardiovascular symptoms, andseventeenwithcutaneous allergic reactions—most followed massive DEET ingestions or topical applications.⁸-¹⁰ Koren et al. reviewed the effectiveness and safety of DEET products in young children, and found only ten reports of seizures in children following topical applications. The investigators concluded that since seizure disorders are diagnosed in 3-5% of children and an estimated 23-29% of children are exposed to DEET, these 10
ADVERSE EFFECTS OF PICARIDIN
Compared to DEET, picaridin is not oily and is more pleasant when topically applied. Picaridin does not have a strong odor and does not damage clothing or plastics.¹³ Five to ten percent concentrations of picaridin are recommended as effective alternatives to DEET in children.¹⁴ The Canadian Committee on Tropical Medicine and Travel considers picaridin among the best
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