For those looking to avoid toxic chemicals like DEET or permethrin (a possibly carcinogenic insecticide frequently used to treat clothing and mosquito nets), plants might hold the key to repelling mosquitoes. One of the most often cited is lemon eucalyptus. In fact, a 2014 Australian study found that a mixture of 32 percent lemon eucalyptus oil provided more than 95 percent protection from mosquitoes for three hours, compared to a 40 percent DEET repellent that gave test subjects 100 percent protection for seven hours.

But lemon eucalyptus is not the only option. A 2013 study examined the ability of 20 different plant essential oils to repel malarial mosquitoes. Notably, rosemary, lemon, eucalyptus, neem, and pennyroyal each had no repellent effect. The three best were cinnamon, citronella, and thyme, which were repellent, irritating, and toxic to the mosquitoes. Additionally, they found that cumin, lemongrass, coleus, and thyme were irritants to the mosquitoes at all concentrations. Another 2013 study found that cinnamon repelled the Asian Tiger mosquito, and so did a plant called Herba Schizonapetae that is used in Chinese medicine. Yet another plant that proved effective in studies is Nepeta parnassicus, a species in the mint family related to catnip.

Unfortunately, plant based products evaporate quickly, which means they must be re-applied. But another study, published in 2001, tried the novel step of adding vanillin to the essential oils it tested on several species of mosquitoes. Vanillin, the primary component of vanilla (which is sometimes created synthetically and used as cheap vanilla flavor), extended the efficacy of the four plants tested (turmeric, kaffir lime, citronella and hairy basil). One commercial product that makes use of this finding is Dr. Mercola’s Bug Spray, which combines citronella, lemongrass, peppermint, and vanillin.