The most effective insect repellent is DEET (N,N-diethyl-m-toluamide), which has been in use as an insect repellent since 1957.  DEET comes in concentrations ranging from 4% to 100%, and appears to work better up to a concentration of 30%, after which it simply lasts longer.  Products containing 10% DEET works for about 2 hours, 24% DEET works for about 5 hours, and over 30% DEET lasts 8 to 12 hours.

The side effects of DEET include hives and skin irritation, although these side effects have generally been reported with chronic overdosing.  There are a few rare reports of seizures, most of them related to very high doses of DEET.

The American Academy of Pediatrics recommends that DEET concentrations of up to 30% are considered safe for children over two months of age.

Our recommendations on DEET use:

• Older children can have 20%-30% DEET applied.  Younger children and infants should have lower concentrations applied.
• DEET is not approved for under 2 months of age.  For children under 1 year of age, you should consider using other protective measures such as netting, long sleeves and pants, and avoiding outdoor activity during high insect activity (e.g. dawn) before using DEET.
• Apply the lowest amount of DEET that will be effective for the amount of time spent outdoors.
• Apply DEET sparingly on exposed skin.  Do not use under clothing.
• Do not apply DEET to the hands and mouths of very young children.  For older children, apply to face by rubbing product on with adult hands; avoid eyes and mouth.
• Apply DEET no more than once a day and wash skin after use.
• Do not use a combination DEET/sunscreen product as sunscreen needs to be re-applied regularly.
• Do not use DEET over cuts, wounds, or irritated skin.