Prior to the COVID-19 pandemic, prolonged face mask use was reserved for a small proportion of society. With their use now widespread, face masks may been anecdotally linked to a range of outcomes, including the worsening of heat stress. In response, a study published on October 9 addressed the impact of face mask use by assessing core body temperature, cognitive performance and a range of perceptual responses during light exercise in hot conditions (40C/20% RH).
Participants reported that perceived shortness of breath was substantially worse with face mask use, whereas core temperature, cognition, skin temperature under the mask, whole-body thermal discomfort and facial thermal discomfort were not adversely impacted. Critics could argue that the exercise duration was not sufficient (45mins), the workload was too low (100W) and that the study had too few participants (n=8). But inadequate heat stress was not an issue given that mean core temperatures were in the 38.2-38.4C range. Results may vary with more prolonged face mask use (just ask passengers disembarking a 4hr flight) but based upon these results, the anecdotal reports of elevated heat stress are yet to be supported by evidence. Note that there are outliers and we expect to see additional research related to this topic.
Morris NB, Piil JF, Christiansen L, Flouris AD, Nybo L. Prolonged facemask use in the heat worsens dyspnea without compromising motor-cognitive performance. Temperature. 2020 Oct 11:1-6.