Summertime hikes and afternoons in the backyard can be ruined by mosquito bites. So, many people apply topical synthetic repellents like DEET before heading outside, but there is a growing market for natural repellants that could be less irritating to the skin and more environmentally friendly. In ACS Omega, researchers describe their new plant-based formulation, a patchouli oil-infused lotion that protected against mosquitoes as effectively as a commercially available DEET formulation.
Unlike many natural repellents that lose effectiveness quickly due to volatility, our formulation achieved complete protection against Aedes aegypti for up to three hours at a relatively low concentration of patchouli oil." - Lizandra Lima Santos
Lizandra Lima Santos
A team of researchers led by Lizandra Lima Santos hypothesized that patchouli oil's rich, earthy aroma - which makes it a popular ingredient in incense and perfume - could act as a sort of invisibility cloak, overwhelming a mosquito's sense of smell and making the wearer undetectable. That's how other bio-based natural alternatives like citronella and eucalyptus oils work, but their ability to prevent mosquito bites doesn't last as long as their synthetic counterparts. Patchouli oil also breaks down quickly when exposed to air, which challenged the team to create a stable formulation for their repellent while preserving the oil's activity. So, they combined patchouli oil with an unscented cream base to create an effective, long-lasting, anti-mosquito lotion.
The researchers asked volunteers to coat their forearms with either the patchouli oil lotion or a commercially available DEET lotion, while one unlucky participant acted as a control with no repellant. Participants then stuck their arms in a cage filled with 50 hungry Aedes aegypti mosquitoes over three hours. The team observed no bites on arms treated with the patchouli-infused and DEET lotions, while the bare arms unsurprisingly had lots of bites. "Unlike many natural repellents that lose effectiveness quickly due to volatility, our formulation achieved complete protection against A. aegypti for up to three hours at a relatively low concentration," says Lima Santos.
One of the most surprising findings was the high level of repellency achieved at a low concentration of patchouli oil. "Natural repellents are often expected to require higher doses to match the performance of synthetic compounds," says Lima Santos, "so observing complete protection for three hours was particularly encouraging."
These initial test results suggest that the patchouli oil cream offers meaningful protection against mosquito bites. Next, the researchers plan to conduct targeted toxicological and clinical studies to determine the new formulation's long-term safety.
The authors acknowledge funding from the Amapá Foundation for Research Support, Research Program of the Brazilian Ministry of Health, Coordination of Improvement of Higher Education Personnel under the Ministry of Education, National Council of Scientific and Technological Development, and the Pro-rector of Research and Postgraduation of the Federal University of Amapá.
