Native North Americans have long used the fragrant herb sweetgrass to ward off biting insects like mosquitoes, and new research shows how the traditional repellent works chemically. About to share their findings with the American Chemical Society, researchers at the US Department of Agriculture, the University of Guelph, and the University of Mississippi report in a press release that sweetgrass contains two chemicals, phytol and coumarin, that appear to be responsible. "Traditional or folk remedies have been a good source of leads for natural things that may be effective in repelling insects," says Charles Cantrell, who works at the USDA's Natural Products Utilization Research Unit; he's also studied breadfruit, beautyberry, and Jatropha, reports the Smithsonian.
Unfortunately, many essential oil repellents only work for 20 or so minutes, he says, and "what we're ideally looking for is something natural and nontoxic that's just as effective as DEET, that will work as an effective repellent for 10 or 12 hours like DEET." Sweetgrass is a meadow grass native to northern climates, reports Discovery. Cantrell's team needs to study the chemicals phytol and coumarin further to see if they will be effective for as long as DEET is, and while sweetgrass didn't turn out to have any previously unknown repelling chemicals (coumarin is already in some commercial repellents while phytol has already been reported on in other studies), at least "now we understand that there's a real scientific basis to this folklore," Cantrell says. (Lemon eucalyptus and black pepper plants may also rival DEET.)