More than a feeling? Impact of face masks on cardiorespiratory parameters and microclimate under the mask in school-aged children

• Face masks alter the thermal microclimate and increase subjective exertion. • FFP2 showed the strongest moderate effects on objective and subjective parameters. • All observed effects were within clinical and physiological limits. Face masks effectively reduce airborne disease transmission, but data on their physiological impact on children remain limited compared to adults. This study evaluates the physiological and thermal effects of surgical masks (SM) and filtering face piece mask (FFP2) on children during typical classroom sessions. In a randomized crossover study with repeated measures conducted in late summer, 39 children (23 girls and 16 boys; age 8–14 years, mean 11 ± 1 years) were monitored during 90-minute school lessons under three conditions: no mask (NM), surgical mask (SM), and FFP2 mask. Continuous recordings included core body temperature (T core ), heart rate (HR), breathing rate (BR), and oxygen saturation (sO 2 ). Additionally, microclimate parameters under the mask, such as relative humidity (RH mask ), temperature (T mask and T skin ), and inhaled/exhaled carbon dioxide (pCO 2in/ex ), were measured. Subjective exertion was assessed using the BORG scale. No significant changes in HR, BR, sO 2 , or T core were observed. Wearing SM or FFP2 mask led to a minor statistically significant, yet clinically irrelevant, increase in pCO 2in/ex (< 2 mmHg) compared to NM. While T mask and RH mask increased significantly (with FFP2 showing higher values than SM), T skin rose only slightly across all conditions. Subjective exertion (BORG) increased marginally with FFP2 masks but remained in the “very slight” range. Wearing SM or FFP2 masks for up to 90 minutes does not impair cardiopulmonary function or oxygenation in healthy children. Observed physiological changes were within normal limits, primarily associated with local thermal effects and minimal discomfort. Face masks are therefore considered safe for short-term use in school settings.