Objective: To determine the protection times provided by insect repellent and sunscreen in combined formulations against biting mosquitoes. To determine if concurrent use of repellent and sunscreen influenced protection times.
Methods: Insect repellent containing comparable concentrations of N, N-diethyl-3-methylbenzamide (DEET) with and without sunscreen were tested on human skin to determine the mean protection time (MPT) against Aedes aegypti (L.) in the laboratory. Further trials were undertaken to determine the effect on MPT of sunscreen reapplication over repellent every two hours.
Results: There was no significant difference in the MPT provided by 80% DEET with (MPT±SE=770±54.8 minutes) and without (MPT±SE=830±20.2 minutes) sunscreen or 7.14% DEET with (MPT±SE =240±15.5 minutes) and 6.98% DEET without (MPT±SE =230±18.4 minutes) sunscreen. Reapplication of sunscreen resulted in a significantly lower MPT of a 17.0% DEET formulation when sunscreen was reapplied concurrently (MPT±SE=330±25.2 minutes), compared with DEET alone (MPT±SE =400±12.7 minutes).
Conclusions: When combined in a single formulation with sunscreen, the MPT provided by both high and low concentrations of DEET is not reduced. However, if sunscreen is reapplied over insect repellent, protection times can be reduced significantly.
Implications: In areas of endemic mosquito-borne disease, the reapplication of a low concentration repellent and sunscreen formulation may provide the most effective protection from biting mosquitoes while minimising the risk of overexposure to DEET.