Grant: Master's Award: Canada Graduate Scholarships

Humans sweat to maintain a consistent internal temperature. Sweat gland expulsion is controlled by the sympathetic nervous system through stimulation of muscarinic receptors. Certain agents may be anticholinergic, and in turn, modify sweat output. Diphenhydramine (DPH), the active ingredient in common over-the-counter antihistamine medication Benadryl, has been identified as a potent anticholinergic drug. However, sparse evidence demonstrates its impact on sweating. Through a double-blind cross-over design, researchers will assess whether DPH, when taken as prescribed, reduces whole-body sweating during exercise heat stress. A total of 20 young healthy adults (10M, 10F) will be recruited to participate. Participants will be asked to consume either a 50mg tablet of DPH or a placebo (e.g. sugar) pill. Two hours post-ingestion, participants will begin walking at a moderate intensity on a treadmill for 60 minutes in hot environments (32C, 50%RH). Whole-body sweating will be calculated from pre and post weigh-ins, accounting for any water lost via respiration. Additionally, core and skin temperature will be monitored throughout the testing protocol to assess whether the hypothesized reduction in whole-body sweating with DPH incurs elevated body temperatures relative to the placebo condition. The implications of this study will be significant for individuals who work or exercise in hot climates, as they may unknowingly be exposing themselves to an increased risk of heat-related illness. Public health bodies currently advise against DPH usage during heat waves, however, despite no systematic evaluation in the literature. Thus, this study could inform workplace safety boards with clear evidence of the relationship between DPH ingestion and suppression of whole-body sweating.