Bug off! Use of insect repellent products in children

June 2002

With the summer months here, it is useful to assess and review available insect repellent products for use in children. While the list of active ingredients in these products is not long, the number of specific products, with their differing concentrations of active ingredients and pharmaceutical dosage forms, may cause confusion among caregivers and clinicians when choosing or recommending a product. This month’s column will review the use of insect repellents for children.

The available insect repellents can effectively repel mosquitoes, ticks, mites, midges, biting flies and fleas. They have relatively little, if any, effect on wasps, hornets, or stinging bees. Insect repellents function by producing a vapor layer that is malodorous or distasteful to insects. This vapor layer extends to approximately to 1.5 inches from skin. Mosquitoes seek out human skin because of carbon dioxide and skin’s odor, moisture and warmth. It’s believed that mosquitoes can locate a human from 100 feet by detecting expired carbon dioxide. Several factors may affect the actual effectiveness of a particular product – wind conditions, perspiration or water that may wash off applied repellent, frequency of application, concentration of the product’s active ingredient, personal body odor of the child, or specific insect species.

Active ingredients

Most insect repellent products contain DEET, N,N-diethyl-meta-toluamide, a chemical synthesized in 1956. DEET is considered the gold standard for insect repellents, as no other substance has been found to be more effective or as active against a variety of insect types. Other agents available in products include soybean oil or citronella oil. These substances, which are often advertised as “natural,” are not as effective as DEET. Products containing DEET are available in concentrations ranging from less than 10% to 100%.

Consumer Reports magazine, a publication of the Consumers Union, tested 20 insect repellent products in 1993. The products were evaluated by applying measured amounts onto the forearms of testers who then inserted their arms into a cage of 500 mosquitoes or 25 stable flies. A technician evaluated the arms for bites at various times. Products with DEET concentrations ranging from 8% to 40% were tested, along with four non–DEET, “natural” products. The product’s staying power for repelling the mosquitoes or flies generally increased with increasing DEET concentration. The most highly rated product effectively repelled the tested insects for more than six hours. The highest scoring non-DEET product ranked 15th out of the 20 products tested. The researchers recommend limiting the DEET concentration in a product to 40% or less for adults, and 20% or less for children. No products, however, with DEET concentrations greater than 40% were tested. The top-ranking products were Ultra Muskol (40% DEET), Cutter Unscented Cream (35% DEET), and Ticks Off! (40% DEET).

Another study (Buescher) evaluated the relationship between DEET concentration and effectiveness against one of the more common species of mosquito in North America (Aedes aegypti). Products with DEET concentrations of 50% were 95% effective for at least four hours. Increasing the DEET concentration to 100% provided less than one hour of additional effectiveness. This data support the Consumer Reports recommendations that products with DEET concentrations greater than 40% to 50% may not be necessary for most users.

Permethrin, an active ingredient in products used for the treatment of head lice, is an insecticide and repellent. It can be effectively used (Permanone, Duranon) to repel mosquitoes and other insects when sprayed on clothes, sleeping bags, or tents. It should not be directly applied to skin. Use of DEET-containing products together with a permethrin-containing product may be the most effective means of repelling mosquitoes and other insects.

Adverse effects

Concerns have been raised about the potential for serious toxicity with DEET. In 1989 a report of seizure activity in four children and one adult possibly related to DEET use was published (MMWR). The children, ages 3–7 years, were previously healthy and had complete recoveries. Exposures to varying concentrations of DEET occurred, with most having less than three applications of the product. In this report other published cases of toxicity are described – a total of six children (17 months–8 years of age). Symptoms of the potential DEET toxicity included behavioral changes, ataxia, encephalopathy, seizure activity and coma. Three of these children died. A report from the Public Health Service in 1986 describes irritability, confusion and insomnia occurring in employees of the Everglades National Park after using repeated applications of DEET. An analysis of more than 9,000 calls to poison centers related to DEET exposure from 1985–1989 concluded that the risk of serious toxicity is minimal.

The above reports indicate the potential for significant toxicity with use of DEET-containing products, although much is unknown about these reports, such as DEET concentrations of the products used by the case patients, application frequency and technique, or systemic DEET concentrations in relation to toxicity. DEET is commonly used, and it has been estimated that 200 million people use DEET–containing products annually worldwide. The relative lack of numerous reports of significant toxicity in relation to this common use of DEET is reassuring, although other cases of adverse effects or toxicity may go unreported. It has been shown that DEET is partially absorbed through skin, and it has been used to enhance the dermal delivery of other drugs.

The appropriate use of DEET-containing products and other means to repel insects includes:

• not wearing bright-colored clothing
• not using perfume or scented body lotions
• not wearing jewelry or other shiny articles
• using only enough insect repellent to cover the skin; 2-4 tablespoonfuls are suggested for an adult (to cover arms, legs, and face)
• not applying insect repellents to children’s hands, or near eyes, or on lips or intact skin
• and once indoors, washing areas well with soap and water where DEET was applied.

Users of insect repellent products should consider that DEET may damage certain clothing materials (synthetics), leather, plastics (eg, eyeglasses, watch crystals), or vinyl car seats.

It is believed that DEET may decrease the effectiveness of sunscreens. Combination products are available and are formulated to provide efficacy as insect repellents and sunscreens. Both the AAP and the American Academy of Dermatology recommend using products containing no more than 10% DEET for children, although the basis for this recommendation is unclear. Products containing no more than 40% to 50% DEET are recommended for adults.

Products

Numerous insect repellent products are available (Table). Most contain DEET, which has been shown to be more effective than products with other ingredients. Products vary by DEET concentration, pharmaceutical dosage form (lotion, aerosol, pump spray, application stick, or cream), and cost. Several products are also available with sunscreens. Some products are directed toward use in children. When choosing a product one should consider the concentration of DEET in the product, pharmaceutical dosage form desired, cost and necessity of a sunscreen.

For more information:

• Brown M. Insect repellents: an overview. J Amer Acad Dermatol.1997;36:243-9.
• Bug off! How to repel biting insects. Consumer Reports. 1993:451-4.
• Oransky S. Seizures temporally associated with use of DEET insect repellent – New York and Connecticut. MMWR. 1989;38:678-80.
• Buescher MD. The dose-persistence relationship of DEET against Aedes aegypti. Mosquito News. 1983;43:364-6.
• Veltri JC. Retrospective analysis of calls to poison control centers resulting from exposure to the insect repellent N,N-diethyl-m-toluamine (DEET) from 1985-1989. J Toxicol Clin Toxicol. 1994;32:1-16.