My opinion

By Dr. Deepak Gupta
Corresponding Author Dr. Deepak Gupta
Wayne State University, - United States of America 48201
Submitting Author Dr. Deepak Gupta

In-Mask Micro-Climate, Indoors, Outdoors

Gupta D. My In-Mask Micro-Climate's Hot And Humid Efficiency. WebmedCentral INFECTIOUS DISEASES 2021;12(1):WMC005693

This is an open-access article distributed under the terms of the Creative Commons Attribution License(CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submitted on: 31 Jan 2021 05:12:05 AM GMT
Published on: 31 Jan 2021 05:34:42 AM GMT

My opinion

Since the dawn of COVID-19 pandemic, I have been personally exploring my masks’ ambiance. After documenting in-mask heat and humidity objectively determined with Hygrochron iButton DS1923 in my face covering [1], I had been wondering whether my in-mask micro-climate will differ (A) if simple mask vs. valved mask vs. N95 mask, and (B) if indoor vs. outdoor. Hereby, image (A) is my in-mask micro-climate over one-hour period on day-(A) with simple mask, valved KN95 mask, and surgical N95 mask, worn for 20 minutes each. Subsequently, image (B) is my in-mask micro-climate over one-hour period on day-(B) with simple mask covering surgical N95 mask (dual mask) worn while indoor with no air changes, indoor with some indeterminate air changes, and outdoor, for 20 minutes each. Irrespective of mask type or ambient environment, images (A-B) demonstrate variable but definite in-mask increases in temperature and relative humidity as measured by Hygrochron iButton DS1923 and absolute humidity as calculated by online calculator [2]. Moreover, based on variabilities in entrapped heat and humidity under mask and such microclimates’ corresponding efficacy to potentially inactivate SARS-CoV-2 [3-5], I can hypothesize that my hypothesized “therapeutic” effect of in-mask micro-climate against “cold” viruses may have variable onset and effectiveness according to mask type [6]. However, it remains to be seen if (and how) barometer readings change under mask, indoor vs. outdoor, considering barometric pressure’s effect on calculated absolute humidity [2], because as noted while outdoor (B), calculated absolute humidity did not budge much as compared to indoor even when measured relative humidity increased in response to decreasing temperature outdoor as compared to indoor. A point worth noting may be that, during heated and dried indoors during winters, the problem may be the low absolute humidity created by cold outdoors whereby heating the indoors further drastically decreasing indoor relative humidity due to the low absolute humidity therein to begin with. However, this problematically low absolute humidity too may somewhat get countered by the somewhat stability in the absolute humidity exhaled by bodies within the masks’ enclosed microclimates irrespective of ambient climates’ labile temperature, labile barometric pressure and labile humidity, outdoors or indoors [7].    



  1. Gupta D: Living with in-mask micro-climate. Med Hypotheses 2020; 144:110010.  
  2. PlanetCalc: Relative humidity to absolute humidity and vice versa calculators.    
  3. Morris DH, Yinda KC, Gamble A, et al: Mechanistic theory predicts the effects of temperature and humidity on inactivation of SARS-CoV-2 and other enveloped viruses. Preprint. bioRxiv. 2020; 2020.10.16.341883.
  4. U.S. Department of Homeland Security: Science and Technology: Estimated Airborne Decay of SARS-CoV-2 (virus that causes COVID-19). ce-and-technology/sars-airborne-calculator
  5. 95.3 WBCKFM: Increased temperature, humidity, and sunlight are detrimental to SARS-CoV-2 in saliva droplets on surfaces and in the air. https://wb
  6. Gupta D: "Therapeutic" facemasks. Med Hypotheses 2020; 143:109855.
  7. Leivo V, Kiviste M, Aaltonen A, Turunen M, Haverinen-Shaughnessy U: Air Pressure Difference between Indoor and Outdoor or Staircase in Multi-family Buildings with Exhaust Ventilation System in Finland. Energy Procedia 2015; 78:1218-23.

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