Consumer Reports recruited volunteers to test out spray-on repellents made of DEET, oil of lemon eucalyptus, picaridin, a chemical called IR3535, and products made with natural plant oils. After the repellents were applied and allowed to sit for 30 minutes, the volunteers reached into a cage containing (disease-free) mosquitoes or ticks.
Two products emerged on top and were able to keep mosquitoes and ticks away for at least seven hours: products that contained 20 percent picaridin or 30 percent oil of lemon eucalyptus. Picaridin resembles the natural compound piperine, an essential oil in black pepper.
However, picaridin is not a natural compound; it’s produced synthetically in the lab. According to the Environmental Working Group (EWG), picaridin does not carry the same neurotoxicity concerns at DEET, although it has not been tested much over the long term. They report:2
“Overall, EWG’s assessment is that Picaridin is a good DEET alternative with many of the same advantages and without the same disadvantages.”