DEET insect repellent: effects on thermoregulatory sweating and physiological strain

Insect repellents (e.g. N,N-diethyl-m-toluamide or DEET) applied to the skin can potentially interfere with sweat production and evaporation, thus increasing physiological strain during exercise-heat stress. The purpose was to determine the impact of 33% DEET lotion on sweating responses, whole body thermoregulation and thermal sensation during walking exercise in the heat. Nine volunteers (2 females, 7 males; 22.1 ± 4.9 years; 176.4 ± 10.0 cm; 79.9 ± 12.9 kg) completed 5 days of heat acclimation (45°C, 20% rh; 545 watts; 100 min/day) and performed three trials: control (CON); DEET applied to forearm (DEET(LOC), 12 cm(2)); and DEET applied to ~13% body surface area (DEET(WB),). Trials consisted of 30 min walking (645 watts) in 40°C, 20% rh environment. Local sweat rate (SR), onset and skin wettedness were measured in DEET(LOC), and heart rate (HR), rectal temperature (T (re)), skin temperature (T (sk)), RPE, and thermal sensations (TS) were measured during DEET(WB). No differences (p > 0.05) were observed between DEET(LOC) versus CON, respectively, for steady state SR (1.89 ± 0.44 vs. 2.09 ± 0.84 mg/cm(2)/min), SR area under the curve (46.9 ± 11.7 vs. 55.0 ± 20.8 mg/cm(2)), sweating onset, or skin wettedness. There were no differences (p > 0.05) in HR, T (re), T (sk), Physiological Strain Index, RPE or TS between DEET(WB) versus CON. DEET did not impact measures of local forearm sweating and when applied according to military doctrine, did not adversely impact physiological responses during exercise-heat stress. DEET can be safely worn during military, occupational and recreational activities in hot, insect infested environments.