Effective insect repellent formulation in both surfactantless and classical microemulsions with a long-lasting protection for human beings.

The aim of this work is to develop a new generation of repellent products with a long-lasting protection based on a natural component, para-menthane-3,8-diol (PMD). The active is first rendered sol. in a surfactantless microemulsion (H2O/iPrOH/PMD) and then in classical microemulsions. The presence of self-assocd. nanostructures is detected by dynamic light scattering (DLS). A synergetic system of surfactants (Cremophor RH40 and Texapon N70) is used. Addnl., 2-ethylhexane-1,3-diol and Et (-)-(S)-lactate are incorporated. The final product contains, as main components, 46% of H2O, 25% of iPrOH, 20% of non-H2O-sol. PMD, and only 4% of surfactants. Investigations of lasting protection on human volunteers are carried out using a cage test bioassay protocol and Aedes aegypti mosquitoes. A complete protection of 315 min is found on the test persons using the surfactantless microemulsion. An extension is obsd. with the final formulation to reach a mean of complete protection of 385 min. This study demonstrates that alternative formulations using a natural active instead of synthetic chems. like N,N-diethyl-m-methylbenzamide (DEET) can be efficient for human protection against mosquitoes.