Summertime considerations – bugs and sun

June 2005

With summer just around the corner, it is timely to review two important summer topics – sunscreens and insect repellents. There are numerous sunscreens and insect repellents available over-the-counter (OTC) and caregivers may become confused when attempting to choose an appropriate product for their child. Clinicians can offer recommendations to assist caregivers with product choice and appropriate use of these products.

Although several insect repellents are available in OTC products, DEET (N,N-diethyl-meta-tolumide) is the most effective. DEET continues to be recommended as an effective repellent against mosquitoes and other biting insects. Clinicians should recommend insect repellents as part of an effective strategy to avoid West Nile virus (WNV) illness, which is spread most commonly by an infected mosquito. Mosquitoes are carriers of WNV, and they become infected after feeding on infected birds. While other ingredients, such as citronella or soybean oil, are available, their duration of effect does not favorably compare to DEET. Recently, however, the CDC adopted two additional insect repellents as effective alternatives to DEET – picaridin and oil of lemon eucalyptus. These ingredients have shown efficacy comparable to lower concentrations of DEET. The Environmental Protection Agency (EPA) regulates insect repellents and has determined that picaridin and oil of lemon eucalyptus are safe and effective. Picaridin, a synthetic insect repellent, has an advantage over DEET by not damaging synthetic fibers in clothing, as DEET may. DEET may also damage plastics (eg, eyeglass frames), synthetic fabrics (eg, rayon, spandex), leather and some watch crystals. DEET does not damage natural fibers like as cotton or wool. Picaridin is available in a 7% concentration (Cutter Advanced Insect Repellent). Oil of lemon eucalyptus is a plant-based insect repellent, and this may offer an advantage to some caregivers seeking natural products. Products containing soybean oil 2% may also offer an advantage to caregivers seeking natural, non-DEET active ingredients. While soybean oil may repel mosquitoes, its duration has been tested to be approximately 90 minutes, which may be disadvantageous to children spending more time outdoors, which can be common. The duration of mosquito repellent effect of soybean oil 2% is equivalent to DEET 5%.

DEET continues to be recommended and assessed as the “gold standard” mosquito repellent. Numerous OTC products are available that contain DEET, and they differ by the available concentration of DEET contained, ranging from 7% to 100%. DEET provides activity against many species of mosquitoes, fleas, ticks and biting flies. Products containing up to 30% DEET may be used safely on children, and DEET may be applied to infants and children older than 2 months of age, according to the AAP. Increasing concentrations of DEET do not affect efficacy, but they do affect duration of effect. Duration of effect begins to plateau at a DEET concentration of approximately 50%, with a duration of effect of approximately six to 10 hours. DEET 10% provides a duration of effect of approximately two hours, and 30% provides a duration of effect of approximately five to six hours. Thus, products containing up to 30% DEET should suffice for most children who are outdoors during summertime. Permethrin, an active ingredient in products used for the treatment of head lice, is an insecticide and repellent. It is available in products (Repel Permanone) that can be used to repel mosquitoes and other insects when sprayed on clothes, sleeping bags or tents. It is not meant to be applied directly to skin.

When applied according to product labeling and in concentrations of 30% or less, DEET is safe to use in infants older than 2 months of age and children. DEET has been extensively tested for safety. The regulatory body of DEET, the EPA, has determined that DEET is safe and effective. While several case reports of toxicity in children have been reported, unknown information about these cases includes application technique and frequency of application. Because DEET is frequently used, the overall lack of commonly reported serious adverse effects supports the general safety of DEET. DEET should generally be applied no more than once daily. If children are outside longer than anticipated, longer than the expected duration of effect of the DEET-containing product applied, and if they begin to be bitten by mosquitoes, an additional application can be used. DEET is water insoluble, and swimming should not necessarily require reapplication. If an increase in mosquito biting after swimming is noticed, an additional application of insect repellent may be necessary.

Appropriate use of a sunscreen product involves more than just choosing a product with the highest SPF rating on the pharmacy shelf. Sunscreen products should be used as part of a complete sun protection program, also incorporating avoidance of peak sun activity and use of protective clothing and hats. Ultraviolet (UV) radiation most damaging to skin includes UVA (320-400 nm wavelength) and UVB (290-320 nm wavelength). UVB is most active at producing erythema. A sunscreen SPF (sun protection factor) corresponds to protection against UVB. UVA can still promote skin damage, and is more responsible for aggravating photosensitivity disorders. A sunscreen product with broad protection against UVB and UVA is most protective to skin, although not all products provide ingredients protective against UVB and UVA. Products providing broad UVB, and UVA protection are best used, and the product’s labeling should state this protection. Sunscreen use is especially important for children, as 80% of lifetime sun exposure typically occurs prior to 18 years of age.

Numerous sunscreen products are available OTC for caregivers to choose from. These products contain at least one of 16 active ingredients. The majority of these ingredients function to absorb UVR, thus blocking its transmission to the epidermis. Two ingredients — titanium dioxide and zinc oxide — function as physical barriers, reflecting UVR. These ingredients provide the broadest UVR protection (290-770 nm). The characteristic of sunscreen products most familiar to caregivers is likely the SPF. SPF is defined as the ratio of the minimal erythema dose (UVR required to produce perceptible redness) with use of a sunscreen to the minimal erythema dose without sunscreen use. Use of a sunscreen provides protection for a defined period as determined by the SPF. Use of a sunscreen with SPF 15 would allow one to be exposed to the sun’s rays for 150 minutes before development of erythema if the same degree of erythema would develop in 10 minutes without use of sunscreen. Sunscreen products are available with SPF of below 10 to 30+. A product with SPF rating of 15 should suffice for most children and adults, even those who burn more easily. Caregivers may believe that a higher SPF rating equates with greater sun protection — a belief that is partly true, yet with significant limitations. Higher SPF ratings primarily provide longer protection, not an inherently greater amount of protection. Using a sunscreen product with broad UVB and UVA protection is also important.

An important consideration for the appropriate use of sunscreens that is often overlooked is proper application. The most common means whereby caregivers misuse sunscreens are application of an inadequate amount of sunscreen and infrequent application. The average adult should apply 9 portions of approximately 1/2 teaspoonful each (approximately 1 ounce total) to skin surfaces likely to be exposed to the sun. While younger children may require less, this dose estimation is still useful. Application of an insufficient amount of sunscreen can decrease a product’s SPF rating by 50% or more (eg, application of too little SPF 15 may result in SPF 7-8 protection). Sunscreens should be applied 30 minutes prior to sun exposure, as this time is necessary for the active ingredients to bind to the skin. An additional important consideration that is often overlooked by caregivers relates to frequency of application — sunscreens should be reapplied every two hours, regardless of SPF rating, as activity and perspiration can diminish the protective effects of applied sunscreen. By definitions established by the FDA, “water resistant” or “sweat resistant” products retain their SPF rating for 40 minutes, and “very water resistant” products retain their activity for 80 minutes. Thus, frequent reapplication is still necessary with products using this labeling. AAP officials have stated that sunscreen products can be safely applied to infants as young as 6 months of age. When insect repellents and sunscreens are used together, the sunscreen should be applied first. Combination products of insect repellents and sunscreens generally are best avoided. Reapplication of sunscreen does not necessitate additional application of insect repellent. Caregivers should be reminded that sunscreen use is just part of sun protection – sun avoidance, especially during peak hours, and protective clothing should also be employed.

The published literature highlights important information on the use of sunscreen products and overall sun protection. A recent survey of more than 10,000 adolescents 12 to 18 years of age (Geller, 2002) on their activities related to sun exposure indicated that only 34.4% reported using sunscreen. Eighty-three percent of adolescents reported experiencing at least one sunburn during the previous summer and 36% reported experiencing at least three sunburns. A survey of more than 800 members of the AAP (Balk, 2004) on their sun protection counseling practices to patients revealed that only 22.3% reported counseling most patients in all age groups. Thus, while many effective sunscreen products are available, they often may not be used at all or when used, they may be applied inappropriately. Clinicians should provide counseling to their patients to insure appropriate sunscreen use.

For more information:

• CDC. CDC adopts new repellent guidance for upcoming mosquito season. April 28, 2005. www.cdc.gov/od/oc/media/pressrel/r050428.htm.
• Fradin MS. Comparative efficacy of insect repellents against mosquito bites. N Engl J Med. 2002;347:13-18.
• Geller AC. Use of sunscreen, sunburning rates, and tanning bed use among more than 10,000 US children and adolescents. Pediatrics. 2002;109:1009-14.
• Balk SJ. Counseling parents and children on sun protection: a national survey of pediatricians. Pediatrics. 2004;114:1056-64.

• Edward A. Bell, PharmD, BCPS, is an associate professor of pharmacy practice at Drake University College of Pharmacy and a clinical specialist at Blank Children’s Hospital, Des Moines, Iowa.