Question: Are see-through face shields as effective as face masks at preventing COVID spread?

Answer: We do not have much scientific evidence directly comparing the effectiveness of face shields versus face masks for preventing the spread of SARS-CoV-2. Based on what we do know, face masks — specifically N95s and surgical masks — offer more protection as compared with face shields. Unfortunately, we have limited data about homemade masks as compared with face shields. And it’s important to note that face shields have some unique benefits. If I had to sum up — 1) both are good, but N95 and surgical masks are better; 2) if you find that you are having trouble consistently and correctly wearing face masks, face shields are a next-best alternative; 3) since most of us are wearing homemade masks rather than N95s or surgical masks (we’re still trying to keep the supply for healthcare workers) we need to pay good attention to fit — evidence shows that mask fit plus tight fabric weave and multiple fabric layers are key to effectiveness; 4) we do not have enough information to compare homemade masks and face shields.

• Face masks are better at preventing airborne spread. Because face shields leave gaps/openings on the sides and bottom of your face, they are less effective at limiting airborne spread of the virus. A recent systematic review published in Lancet showed that while both face masks and face shields limit the spread of SARS-CoV-2, face masks are more protective. Additionally, a 2014 study published in the Journal of Occupational and Environmental Hygiene of the effectiveness of face shields at protecting healthcare workers from influenza infection concluded that, “face shields provide a useful adjunct to respiratory protection for workers caring for patients with respiratory infections. However, they cannot be used as a substitute for respiratory protection when it is needed.” Note: face masks in these papers are N95s or surgical masks.
• Face shields offer eye protection. There is some evidence that the coronavirus can be transmitted through the eye (see Q&A of 4/4), though this transmission route seems far less common. Still, the eye protection offered by face shields is a benefit of this type of personal protective equipment.
• Face shields may be more user friendly — easier to consistently and correctly use. Face shields make communication easier (you can see a person’s face). They may also be more comfortable to wear, which may keep users from touching their faces or inappropriately removing the shield. For more on these behavioral considerations, see this recent JAMA viewpoint article, this NY Times article, this People article, and this AARP Magazine article and this visualization from Business Insider(Figure 1).

Figure 1. Face Masks vs. Face Shields (visualization from Business Insider based on JAMA viewpoint)