 [ Symptoms ] what are the guidelines for using insect repellent on a baby [ Disease ] unlike sunscreen which is important to reapply every few hours insect repellent generally should be used just once a day and then washed off before bedtime check labels for age recommendations deet is approved for infants over 2 months oil of lemon eucalyptus is not recommended until at least 3 years higher concentrations of deet last longer than lower ones 10 deet is effective for 2 hours while 24 is effective for about 5 the american academy of pediatrics recommends that children use deet concentrations below 30 deet and picaridin tend to last longer than plant oil based repellents you can also use netting to physically keep bugs away from your baby 