In 2018 Consumer Reports conducted clinical trials on brave employees in order to evaluate insect repellents for their ability to protect against mosquito bites and ticks. The most effective active ingredients tested were DEET, oil of lemon eucalyptus, and picardin. Interestingly, other natural repellents such as citronella were found to offer relatively poor protection.
DEET was most effective when formulated in a 15 to 30 percent concentration, and consumers should avoid using this product on babies younger than two months of age. Oil of lemon eucalyptus was most effective when formulated in a 30 percent concentration, and the F.D.A. recommends against using the product on children younger than three years old. Picardin is chemically related to a product of the black pepper plant and was most effective in a 20 percent concentration. Picardin was also most effective when formulated in a spray vehicle. All products were deemed safe during pregnancy when used as directed. Recommended insect repellents are published on www.consumerreports.org.
Notably, products should be applied to either exposed skin or to clothes, but not to skin under clothes. Moreover, when applying a repellent to the face, spray it onto the hands first, then rub it in, avoiding the eyes and mouth.