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 cm²); 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/cm²/min), SR area under the curve (46.9 ± 11.7 vs. 55.0 ± 20.8 mg/cm²), 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.