Preamble:  In an attempt to maximize the wear time and comfort of our SAGE REBREATHER™ line of rebreathing masks, we found it necessary to tackle the issues of present-day masks and physiologies. It was this effort that led to the FACESHIELD™, a “clever” technology that has real promise to change the world of all masks, worldwide.

 Defining the problem:

In a 2020 interview, Eric Toner, a senior scholar at the Johns Hopkins Center for Health Security, notes that, “Americans will be wearing masks for ‘several years” to come.[1] Billions upon billions of facial masks were worn around the world even before the COVID-19 pandemic struck the planet. One company, 3M, announced plans to manufacture 1-2 billion masks annually. The world has indeed changed. Masks are now de rigueur for virtually everyone in some form and at some time during their day. Further, certain professions are required to wear a facemask nearly non-stop (e.g., servers, greeters, medical professionals, and the like).

The concept of the FaceShield™ was born out of necessity. We encountered a design challenge in that our SAGE REBREATHER masks, for COVID-19 management, would be required to be worn for prolonged periods (many hours per day) to improve the effectiveness of the physiological benefits offered by rebreathing CO₂. We know, however, mask tolerance leaves much to be desired, and we determined, through literature searches, that the reasons for that are multi-factorial.

“The area of the face that is covered by Protective Facial Masks (PFMs) is very thermosensitive“ (Laird et al. 1999). When comparing regional nerve ending density, the dermal structures of the face exist with heat sensory nerves numbering some 100 times more than \regions like the hands and feet. Further, thermography of the face confirms that certain regions of the face (the cheeks just under the eyes and around the nose and mouth) experience physiologically cooler temperatures in normal individuals (FIG 1). “One of the more frequently cited reasons for intolerance and lack of compliance with appropriate PFM use is the discomfort related to buildup of facial heat” (Jones, 1991; Laird et al., 2002; Radonovich et al., 2009).

(Fig 1) Human thermography with Red (temples and neck) areas portraying temperatures above 93° F, Green (forehead, eyes, and chin) being under 90° F, and Blue (cheeks) being well below 89° F.[2]

The term “humidex” was first coined in 1965[3] and then what followed was the concept of a “HEAT INDEX,” which was first conceived by Robert G. Steadman in 1979[4] and has been fully accepted and utilized worldwide by weathermen (meteorologists) for more than 40 years. The algorithms used to calculate a heat index are based on the fact that moisture vapor represents such a a great conductor of heat; therefore, both heat and humidity are heavily weighted in these formulas. Humidity means such a comfort issue such that when we see steam (moisture) used in autoclaving (sterilizing instruments), the total heat of the autoclave can be reduced from 170° C (for 60 minutes) down to 120 C (for just 15 minutes) and still ensure sterility.[5] The physics of moisture vapor (humidity) behind a protective facial mask shows us how devastating to what the human skin can tolerate. Additionally, human exhaled breath exists at 100% and more than 90° F.

The medical literature makes it quite clear that the skin’s intolerance of combined heat and humidity does not help keep the skin healthy. The National Weather Service and FEMA describe EXTREME Heat Safety Disorders when one experiences prolonged Heat Indexes at 130 and above.[6]—equivalent to 100% humidity and 90° F, which we know represents the EXACT environment behind ALL masks. The body cannot dissipate its heat in this environment. We utilized probe hygrometers and thermometers to test and calculate the Heat Indexes of some 20 different commercially available masks. All of them have a heat index ABOVE 130.

Taken from The National Weather Service and FEMA⁵

“Mask” (acne under the mask) – is a term coined for breakouts caused by a mask’s hot, humid environment.[7] The Mayo Clinic weighed in on the occurrences of skin irritations from covers. Dr. Dawn Davis, a Mayo Clinic dermatologist, “Maskne happens because of natural wear but also because the masks are tight, which is well-intentioned, but can strangulate the skin.”[8] Pointing out that heat, moisture and friction contribute to skin irritations. Also, “When you exhale air while wearing a mask, the air has no choice but to travel upwards towards your eyes. Of course, this triggers , and you get the urge to rub your eyes.”[9] Bringing your hands to your face in a pandemic does not represent good infection control methods.

So, the issues we seek to mitigate with this effort include the following:

1. Exposure to heat and humidity (for both long and short term)—THE MOST critical.
2. The friction of facial structures due to mouth or jaw movement causes harder mask surfaces to abrade the skin or add to leakage.
3. Tugging on ears
4. Air jets into eyes
5. Creating a generally better seal to the face

DeltaChase answers to the above challenges follow:

1. Heat and Humidity: We intend to literally BLOCK the heat and humidity from imparting the damaging “heat index” back onto the most sensitive portions of the face. To do this, we must create a new “microclimate” under the FaceShield that insulates the skin from the effects of heat and humidity. We designed the Face Shield to cover more than 90% of the facial structures, normally making contact with the hot, moist, exhaled breath. Of the parts not protected, the nose and lips make up the larger segment, and they naturally resist heat and humidity because they are mucous mucosa, not squamous epithelia.
   1. The textile used to form the FaceShield may contain technologies to actually COOL the skin in their own right.
      1. Heat transfer can come about by way of four mechanisms
         1. Emissivity/Effusivity (the wavelength and amplitude determined by the material make-up of the object itself). Metals have low emissivity, while skin has high emissivity.
         2. Radiation (mostly determined by the core temperature of the object).
         3. Conductance (the objects must necessarily be in contact to “conduct” heat transfer).
         4. Convection (movement of air flow to transfer heat)
      2. Presently, samples of commercially available Brrr°, ISO-Chill and COCONA (37.5°) have been tested for optimization of their cooling effects under facemasks.

3. Friction: The Face Shield is designed to utilize 4-way stretch materials and those that are warp weaved to attain this. Ideally, the stretch is greater than 200% in all directions and may encroach 400% stretch. Further, Nylon or “nylon-like” materials have been chosen as the luxurious feel, excellent wicking, and moisture control assist in creating a microclimate UNDER the FaceShield™ that is far superior to the “blast furnace” gases created by exposure to exhaled air.
   1. Footprint contemplation, like a wavy edge around the oral/nasal orifice, help to prevent tethering of certain regions of the mask when talking or opening the jaw (to yawn or cough etc.) Without these wavy edges, the mask would more readily pull off the nasal bridge each time one opens the mouth.
   2. One will also note a slit at the bottom of the device where the chin-cup resides, such that when one opens the mouth or jaw, it will not so readily pull the entire mask downwards
4. Tugging on ears: Likewise, the ear openings are not uniformly created as circles or ovals as the forces of stretching the entire shield over the ears would normally lead to pulling the mask upwards towards the superiorly placed ears (in relation to the lower mouth and jaw). So, a larger portion of the “ear-loop” is directionally positioned upwards to reduce tethering and pulling of the entire mask upwards (superiorly)
5. Air jets into the eyes: Will be handled by folding over the top portion of the device and sealing over into a cavity positioned to the right and left of the nasal opening, to stuff with foam rubber, beads, threads or spongey material to create a grommet or dam to block the passage of exhaled air between the nose and cheek (at the nasolabial fold)
6. Darts are positioned (laterally and inferiorly) to allow for the fabric to better lay down and seal/conform with the skin. Creasing and bending of the fabric could allow the hot moist gases to find their way under the Shield thus defeating our purpose.
   1. Creating a seal under a CPAP mask represents a bit more of a challenge, as one has to handle pressure gradients in addition to heat and humidity.
   2. A CPAP leak presents a double-edged sword, since the leak diminishes efficacy of the device and the leek can cause irritation into the eyes.
   3. We see the typical pressure experienced during CPAP use at 10 cmH₂O, however, there are scenarios of patients requiring as much as 20 cm H₂O pressure.
   4. The harder silicone (or rubber-like elastomer) mask itself often does not conform well around the nose and thus air jetting into the eyes is a particular risk and nuisance.
   5. These elastomers may not seal well against a woven textile, so one way to improve this seal is to use spray a sealant or water-proofing agent around the periphery of the FaceShield (where it would come into contact with a CPAP underside) and this will help to form a better pressure tight seal between the FaceShield and CPAP mask.
   6. We do not foresee using this spray sealant over the entirety of the FaceShield as we do not wish to inhibit moisture vapor transmissibility up from the skin.

[1] https://www.foxnews.com/us/coronavirus-expert-says-americans-will-be-wearing-masks-for-several-years
[2] Protective Facemask Impact on Human Thermoregulation: An Overview, ROBERGE, COCA, Ann. Occup. Hyg., Vol. 56, No. 1, pp. 102–112, 2012
[3] Environment and Climate Changes. Government of Canada. Retrieved 22 September 2016 “Spring and Summer Hazards”. 
[4] Steadman, R. G. (July 1979). “The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science”. Journal of Applied Meteorology. 18 (7): 861–873.
[5] www.cptmed.com/differences-between-moist-and-dry-heat-heat-for-custom-trays
[6] https://www.rhsb.com/risk-of-extreme-heat/
[7] https://cw.ua.edu/65524/top-stories/full-time-mask-wearing-brings-its-own-set-of-problems/
[8] https://newsnetwork.mayoclinic.org/discussion/treating-skin-irritations-from-wearing-face-masks/

[9] Face masks for the public during the covid-19crisis, BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m1435 (Published 09 April 2020). Cite this as: BMJ 2020;369:m1435