The primary ingredient in Listerine is eucalyptol, a natural oil that is also an active ingredient in botanical repellents. Several studies, including one from the London School of Hygiene and Tropical Medicine, have found that eucalyptus based repellents can be extremely effective and non toxic to humans. However, the eucalyptus-based repellents contained 75% concentration of the compound and the concentration found in Listerine and other mouthwash is usually below 1%. Listerine is actually .092% eucalyptol. Mouthwashes are usually water and alcohol based which causes them to evaporate quickly. Commercial repellents such as DEET, Picaridin and oil of lemon eucalyptus are formulated to last for hours. While Listerine may ward off mosquitoes momentarily, it will not work as a barrier treatment to prevent mosquitoes around the house and it will not provide protection applied on your skin for very long. Content source: http://www.snopes.com/oldwives/dishsoap.asp
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