An incredible 900,000 types of insects are known to exist. Equally incredible is the number of insect repellents available.
Here is what you should know:
1. The most thoroughly studied insect repellent is DEET.
No repellent bears this name; it is the active ingredient in most products. Don’t be alarmed by its chemical formula, N,N-diethyl-m-toluamide Lots of products used by children have similar formulas, including most “natural” substances. DEET is safe when used correctly and is approved for children ages two months and 
above. Only extreme misuse has caused toxic reactions. Skin rashes do occur, but rarely. DEET repels more types of disease-carrying insects than other substances. (See picaridin below.)
2. DEET comes in all forms and strengths.
There are lotions, creams, gels, aerosols and towelettes. Acquaint yourself with several products. Read instructions. Know the concentration of DEET in the product. Contact manufacturers, if necessary; most have websites.
3. Products containing 20 to 30% DEET are recommended for children.
Higher percentages are effective for longer periods of time but are only marginally more protective, and may be more likely to cause skin irritation.
Periods of effectiveness for various concentrations are as follows:
100% DEET 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.
These results were obtained in a laboratory under controlled conditions. Lasting power is affected by temperature, humidity, sweating, water exposure and other factors. If children require prolonged protection, it is safer to use low-concentrations and reapply as needed. (A microencapsulated, sustained-release formulation may be effective for 8-12 hours with only 20-35% DEET and appears to be safe on children.)
4. Apply DEET to exposed skin only.
There is no need to place it under clothing (and it damages synthetic fibers). Apply repellant to your hands and then rub them on the child. A thin coating is sufficient; more does not increase protection. Avoid eyes, mouth, wounds or rashes. If accidentally applied to such areas, rinse with soap and water. Apply in a well-ventilated area. Wash off when no longer needed.
5. Picaridin-containing repellents appear to be as effective and safe as those containing DEET.
Picaridin was approved in the U.S. in 2001, but has been used elsewhere for longer. It appears to be as effective against as many different species of insects as DEET. In addition, it is fragrance-free and does not need to be washed off when returning indoors.
6. “Natural” products are not necessarily better.
Many such products are available. These too are chemicals and most have not been thoroughly studied. The most popular one is oil of lemon eucalyptus (active ingredient: p-menthane 3,8-diol). Its protective qualities are similar to repellents with low concentrations of DEET. Oil of lemon eucalyptus products are not approved for children less than three years of age.
7. Read labels on products intended for sensitive skin.
Some children have eczema and other skin conditions. Likely, this makes their skin more sensitive to repellents and may increase the amount of repellent absorbed into the body. However, many products made for sensitive skin are poor repellents. Ask your doctor for advice.
8. Avoid products that are useless or inadequately researched.
Wristbands are ineffective. Taking vitamin B merely reduces itching from bites, causing you to think you are being bitten less. Sound and light devices do attract insects to your area, but insects prefer you to the devices, possibly increasing your chances of being bitten. Products which emit vapors may be harmful if inhaled indoors over prolonged periods of time, especially by children. Outdoors, vapor effectiveness depends on wind direction and other factors.
9. Don’t use products that combine insect repellents and sunscreens.
While many situations call for both, the intervals of applications and other considerations make combination products impractical. Generally, apply the sunscreen at least twenty minutes before sun exposure while the repellent can be applied just before exposure. The repellent may reduce the effectiveness of the sunscreen. Consider using a stronger sunscreen.
10. Use DEET and picaridin when breast-feeding.
Where insects carry disease-causing organisms, both mothers and infants must be protected. There are no known harmful effects to infants from drinking breast milk of mothers who are using DEET or picaridin.
