Evaluation of biological and chemical insect repellents and their potential adverse effects

Plant extracts, particularly plant oils, had been used and were still in use as repellents against mosquitoes. Some of them (e.g., lavender, geraniol, and citriodiol) have been notified by the European Commission as active substances to be used in repellents, which are categorized as biocides in product type 19. In the literature, it is known that these substances must be added to repellent products in high concentrations (e.g., 20% and more) in order to reach repellent efficacy. Therefore, the question arose whether they also have repellent effects if they were added as fragrances at low concentrations of 0.25 or 1% to registered active substances in order to obtain a better scent of this product. In the present study, the repellent effects of 0.25 and 1% additions of 15 plant extracts (citronellol, cinerol, citral, menthol, linalyl acetate, Eucalyptus citriodora, Eucalyptus globulus, Cymbopogon nardus, lilac, sandalwood, Vitex agnus castus, rosewood, lavender, geraniol, and paramenthan diol) when exposed on skin to hungry Aedes aegypti mosquitoes. These experiments showed that there was no repellent effect in any of these compounds even when the test was done already 10 min after distributing any of the compounds onto the hands of volunteers. These experiments have proven that these 15 compounds do not produce repellent effects as long as they are used in low concentrations of 0.25 or 1% as fragrances to ameliorate the odor of a notified repellent that is brought onto the skin.