Do Face Masks Contribute to Heat Stress?

Prior to the COVID-19 pandemic, prolonged face mask use was reserved for a small proportion of society. Following their widespread use, face masks have been anecdotally linked to a range of outcomes, including an exacerbation of heat stress. In response, Morris et al. (2020) 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 (40ºC/20% RH).

Participants reported that perceived shortness of breath was substantially worse with face mask use, whereas core temperature, cognition, under mask skin temperature, 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 38.2-38.4ºC (~101ºF) range. Results may vary with more prolonged face mask use, but based upon these findings, 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.

Reference

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;11:1-6.