How Good Are Face Shields for Preventing Respiratory Infections?

Patient Presentation
With the COVID-19 epidemic, several pediatricians were discussing use of their personal protective equipment. Several noted that the face masks were itchy when worn for a long time. One person was complaining that the face shield he was given was giving him a headache and was difficult to wear to complete the ear examination. Another person said, “We know the face masks work for us and for other people who are wearing them to reduce exposures, but do these face shields really work?”

A scoping review of facial protection for health care workers during a pandemic found that respirators such as N95 masks provide excellent protection against viruses and aerosols especially when combined with eye protection. Mask fit is an important consideration and respirators are tight fitting and therefore much less breathable and comfortable to wear for long periods of time. Surgical masks do not provide as much protection as respirators but are in general more breathable and more comfortable. Surgical masks also provide much more protection than no mask or improvised masks. Improvised masks do provide some protection and are better than no masks. A face mask worn by someone who is ill, helps to prevent respiratory secretion aerosolization, and therefore helps to protect those around them.

Face shields have been used to protect health care workers from infection for at least 100 years. Face shields create barriers for “…acutely-expelled aerosols of body fluids and are commonly used as an alternative to goggles as they confer protection to a larger area of the face.” Face shields can offer more coverage and less self-inoculation, have improved breathability and less claustrophobia, often are more comfortable, are easy to put on and off, can be used with other equipment, are reusable, easily cleaned and relatively inexpensive. They can also extend the life of personal protective equipment if used concurrently. Face shields can however get fogged up, have glare, be optically imperfect and can be bulky.

For face shields and for improved protection, more is more. “..[A] full face length with outer edges of the face shield reaching at least to the point of the ear, include[ing] chin and forehead protectors, and cover the forehead.” There should be appropriate space between the provider’s face and the shield to allow appropriate use of other equipment such as eyewear, masks, respirators, etc. The face shields should fit snugly to the forehead. Visors from polycarbonate, proprionate and acetate have good visual clarity for less eye strain. If possible, visors with anti-fogging, anti-static and anti-glare properties provide additional comfort and usability for the wearer.

Once a face shield is chosen, it only works if used properly. The face shield needs to be appropriately placed on the head with the visor in the down position and left there.

As a reminder the recommended donning (e.g. putting on) sequence is performing hand hygiene, gown, facemask, face shield and gloves, and doffing (e.g. taking off) is in the reverse order, remembering to perform hand hygiene. This obviously needs to be changed based on specific protective equipment and the indications for the specific hazard. Equipment then needs to be appropriately discarded or cleaned. Hand hygiene is always important.

Learning Point
Studies of face shields have found the following:

“Lindsley et al. reported 96% and 92% reductions in the risk of inhalation exposure immediately after a cough for a face shield at distances of 18 in (46 cm) and 72 in (183 cm) respectively.” This was for a particle size of 8.5 micrometers or the size of an influenza virus. With a decreased aerosol size to 3.4 micrometers, this still resulted in a 68% blockage by the face shield at 18 inches immediately after the cough and 23% in the 1-30 minutes after the cough. This is the time frame used to judge the amount of droplet particles that would drop out of the air and the amount that would remain airborne and would be able to flow around the sides and bottom of the shield.

Unsurprisingly, when someone coughs, the potential contact with the aerosolized particles is highest just after the cough and highest closest to the coughing source. In Lindsley et al.’s study, the particles generated in the first minute exceeded the detection capacity of the study equipment. This is where face shields work very well, because they can physically block the initial high concentration of aerosolized particles. They especially are good at blocking droplets at close range. Over time though as facemasks are open to the general air, after the droplets fall away, the remaining aerosolized particles can go around the face shield. However, in studies even in this phase they perform a little better than no mask as noted. Although some aerosolizing procedures such as intubation or nasopharyngeal swab testing can be anticipated, no one can anticipate when someone else close to them will cough or sneeze, therefore consistent use of face shields by health care providers can improve protection.

Another study used fluorescent dye with a particle size of 5 micrometers sprayed from a distance of 50 cm (20 inches) found that a face shield that covered face from forehead and including the neck, and laterally to the ears, protected the eyes, nose and mouth from contamination.

Airflow is important because the more air flow or air changes in a room, the quicker the aerosol is diluted. It is estimated that with one air change that 63% of the aerosols are removed, and with each subsequent change an additional 63% are removed. Therefore after 5 air changes, the amount of aerosol is < 1%. This idea is important in health care for understanding how long people may be exposed to the aerosols and for appropriate room cleaning.

Questions for Further Discussion
1. What personal protective equipement (PPE) are you using and how are you actually using it?
2. What measures to ensure adequate PPE and education for how to use it properly are being done in your location?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Occupational Health for Health Care Providers, Germs and Hygiene and Coronavirus Infections.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Bunyan D, Ritchie L, Jenkins D, Coia JE. Respiratory and facial protection: a critical review of recent literature. J Hosp Infect. 2013;85(3):165-169. doi:10.1016/j.jhin.2013.07.011

Lindsley WG, Noti JD, Blachere FM, Szalajda JV, Beezhold DH. Efficacy of face shields against cough aerosol droplets from a cough simulator. J Occup Environ Hyg. 2014;11(8):509-518. doi:10.1080/15459624.2013.877591

Roberge RJ. Face shields for infection control: A review. J Occup Environ Hyg. 2016;13(4):235-242. doi:10.1080/15459624.2015.1095302

Garcia Godoy LR, Jones AE, Anderson TN, et al. Facial protection for healthcare workers during pandemics: a scoping review. BMJ Glob Health. 2020;5(5). doi:10.1136/bmjgh-2020-002553

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa