The effects of wearing facemasks on oxygenation and ventilation at rest and during physical activity

PLoS One. 2021 Feb 24;16(2):e0247414. doi: 10.1371/journal.pone.0247414. eCollection 2021.


Background: Facemasks are recommended to reduce the spread of SARS-CoV-2, but concern about inadequate gas exchange is an often cited reason for non-compliance.

Research question: Among adult volunteers, do either cloth masks or surgical masks impair oxygenation or ventilation either at rest or during physical activity?

Study design and methods: With IRB approval and informed consent, we measured heart rate (HR), transcutaneous carbon dioxide (CO2) tension and oxygen levels (SpO2) at the conclusion of six 10-minute phases: sitting quietly and walking briskly without a mask, sitting quietly and walking briskly while wearing a cloth mask, and sitting quietly and walking briskly while wearing a surgical mask. Brisk walking required at least a 10bpm increase in heart rate. Occurrences of hypoxemia (decrease in SpO2 of ≥3% from baseline to a value of ≤94%) and hypercarbia (increase in CO2 tension of ≥5 mmHg from baseline to a value of ≥46 mmHg) in individual subjects were collected. Wilcoxon signed-rank was used for pairwise comparisons among values for the whole cohort (e.g. walking without a mask versus walking with a cloth mask).

Results: Among 50 adult volunteers (median age 33 years; 32% with a co-morbidity), there were no episodes of hypoxemia or hypercarbia (0%; 95% confidence interval 0-1.9%). In paired comparisons, there were no statistically significant differences in either CO2 or SpO2 between baseline measurements without a mask and those while wearing either kind of mask mask, both at rest and after walking briskly for ten minutes.

Interpretation: The risk of pathologic gas exchange impairment with cloth masks and surgical masks is near-zero in the general adult population.

MeSH terms

  • Adult
  • COVID-19 / prevention & control*
  • COVID-19 / psychology
  • COVID-19 / transmission
  • Carbon Dioxide / metabolism
  • Exercise / physiology
  • Female
  • Heart Rate / physiology
  • Humans
  • Hypoxia / etiology
  • Hypoxia / metabolism
  • Male
  • Masks* / adverse effects
  • N95 Respirators / adverse effects
  • Oxygen / metabolism*
  • Pulmonary Ventilation / physiology*
  • Rest / physiology
  • SARS-CoV-2 / isolation & purification
  • Walking / physiology


  • Carbon Dioxide
  • Oxygen

Grant support

The authors received no specific funding for this work.