Application of insect repellents by travelers to malaria endemic areas

Background. The use of insect repellents applied to the skin is always encouraged in those visiting malaria endemic areas. There are a number of factors contributing to the efficacy of insect repellents in the field and an important factor contributing to their longevity relates to the applied dose. This study investigated the dose of insect repellent that travelers might normally apply to the skin. Method. Subjects were asked to apply a product they had purchased to the arms and neck, and the dose applied (mg/cm(2)) was calculated. The study was conducted using three different populations; 74 travelers to malaria endemic areas visiting pharmacies to purchase repellents before they left the UK, 23 travelers on safari in India, and 24 on safari in Kenya. Results. There was a significant difference in the mean applied arm dose of product (mg/cm(2)) [p < 0.001, analysis of variance (ANOVA)]; UK 1.15 (SD 0.29), India 0.96 (SD 0.23), and Kenya 1.34 (SD 0.54). Higher concentrations were achieved on the neck area. Few of the participants in the field trial used long-sleeved shirts at night. Even using 50% wt/vol repellent products, 32% in the Kenya and 25% in the India, study achieved a dose of active ingredient less than 0.5 mg/cm(2). Conclusion. These pilot studies would indicate that travelers tend to apply below the optimal concentration of active ingredient of repellent as might be suggested by mathematical models.