Repellents containing DEET (N,N-diethyl-3-methylbenzamide) are recommended for areas where travelers may encounter potentially life-threatening mosquito-borne diseases, such as malaria and yellow fever. Products containing lower concentrations of DEET are as effective as those with higher concentrations, but for shorter periods of time. On average, products containing 100% DEET will be effective for 9.5 hours, 30% DEET for 6.5 hours, 15% DEET for 5 hours, 10% DEET for 3 hours and 5% DEET for 2 hours. Controlled release preparations containing 20-35% DEET, such as Ultrathon (PDF), may be effective for 8-12 hours or more. Factors such as high temperature, humidity, sweating, and water exposure may reduce the duration of a repellent's effectiveness.
In general, adults and children greater than 12 years of age should use preparations containing 25-50% DEET. Preparations containing higher concentrations of DEET carry greater toxicity with little additional benefit. Children between 2 and 12 years of age should use preparations containing no more than 10% DEET, applied sparingly. If children require prolonged protection, it is safer to use low-concentration DEET, reapplied when needed, than to use high-concentration products. Neurologic toxicity has been reported from DEET, especially in children, but appears to be extremely uncommon and generally related to overuse. DEET-containing compounds should not be used on children under age two.
The Centers for Disease Control states that the recommendations for DEET use in pregnant women do not differ from those in nonpregnant adults.
Insect repellents should be applied judiciously to exposed skin, though not to eyes, mouth, cuts, wounds, or irritated skin. If this accidentally occurs, the affected area should be rinsed promptly with water. Do not apply to skin under clothing. Do not use repellents in enclosed, poorly ventilated areas or near food. Children should not be allowed to apply their own repellents. Do not apply to children's hands, since they may put these in their mouths. Insect repellents should be washed off with soap and water when no longer needed.
DEET-containing products may also be applied to garments, window screens, mosquito nets, tents, and sleeping bags, though care must be exercised, because DEET may damage certain plastics and synthetic fabrics. If DEET is applied to clothing, the garments should be washed before worn again.
Though less effective, insect repellents containing certain botanical products may be an option when the duration of insect exposure is short or when the risk of contracting a serious infection from mosquito bites is small. A preliminary study in the New England Journal of Medicine found that those containing oil of lemon eucalyptus (Fite Bite Plant-Based Insect Repellent, Travel Medicine; and Repel Lemon Eucalyptus Insect Repellent, WPC Brands) provided protection for an average of two hours, and a product containing soybean oil (Bite Blocker for Kids, HOMS) was effective for an average of 90 minutes. By contrast, repellents based on citronella prevented bites for less than 20 minutes and are not recommended. Oil of lemon eucalyptus should not be used on children less than three years of age.
For additional protection against mosquito bites, products containing permethrin, a contact insecticide, may be applied to clothing, shoes, tents, and bed nets. Studies have shown that permethrin-impregnated bednets are more effective than untreated ones. When bed nets are not washed, the insecticide remains effective for several months. Even when items such as clothing are laundered, permethrin treatments remain effective for at least two weeks. Permethrin should be reapplied after every five washings. There is no signifcant toxicity when applied to clothing, but permethrin should not be applied directly to skin.
Mosquito coils, which fill the room with a vapor of insecticide, may be useful if sleeping in an area not otherwise protected from insects. Coils which contain dichlorodiphenyltrichloroethane (DDT) should be used with caution. Repellent-impregnated wristbands are not effective.
From the Centers for Disease Control (CDC)
Protection against Mosquitoes, Ticks, Fleas and Other Insects and Arthropods
Updated Information regarding Insect Repellents
Insect Repellent Use and Safety
From Health Canada
Safety Tips on Using Personal Insect Repellents
Personal Measures to Prevent Mosquito Bites
From the New England Journal of Medicine
"Comparative Efficacy of Insect Repellents against Mosquito Bites" (Mark S. Fradin, M.D., and John F. Day, Ph.D.; NEJM, July 4, 2002; 347:13-18)
From the American College of Physicians
"Mosquitoes and mosquito repellents: A clinician's guide" (Mark S. Fradin, MD. Annals of Internal Medicine. June 1, 1998;128:931-940)
From the United States Environmental Protection Agency (EPA)
How To Use Insect Repellents Safely
Reregistration of the Insect Repellent DEET
Pesticides and Mosquito Control
From the American Mosquito Control Association