Nearly 700 million people suffer from mosquito-borne diseases—such as malaria, West Nile, Zika and dengue fever—each year, resulting in more than 1 million deaths. Increasingly, many species of mosquitoes have become resistant to the popular pyrethroid-based insecticides. Today, researchers report a new class of mosquito repellents based on naturally occurring compounds that are effective in repelling mosquitoes with potentially fewer environmental side effects than existing repellents.