New testing conducted by Consumer Reports found that for the first time, insect repellents containing milder, plantlike chemicals were most effective against mosquito and tick bites than traditional products.

A total of 15 products were tested and a product failed if a tester was bitten by a disease-free female mosquito two or more times in one five minute session or one in two consecutive sessions. For ticks, the repellant failed if two disease-free deer ticks crossed into treated areas on the volunteers’ arms.

Products containing ≥15% of deet (N, N-diethyl-meta-toluamide) were effective, although concentrations above ≥30% have not been found to be better in repelling insects and may lead to rashes, disorientation, and seizures.  As well, products with low concentrations such as 7% are generally not effective in preventing insect bites.  Deet should not be used at all on infants younger than 2 months.

Picaridin, which is made to resemble the compound piperine that naturally occurs in black pepper plants, and oil of lemon eucalyptus, from the gum eucalyptus tree, have emerged as alternatives to deet in the past decade. Repellents containing 20% picaridin and 30% oil of lemon eucalyptus (p-Menthane-3,8-diol) outperformed those containing deet and kept mosquitoes away for at least seven hours and deer ticks for at least six hours. The concentration is key, as one spray containing only 5% picaridin was less effective than a 7% deet product. Both ingredients have less serious side effects than deet, but picaridin is considered to be a better choice for children since oil of lemon eucalyptus can cause temporary eye injury and should not be used on children under the age of 3. Picaridin, however, may cause some irritation of skin, eyes, and lungs. Citronella candles, wristbands, and products with geraniol, lemongrass, and rosemary oils did not provide much protection against insect bites.