Experts agree that wearing a mask is the most effective way to slow the spread of COVID-19, but not all masks are equally protective. While there is plenty of research about the efficacy of surgical grade masks, there is little research about the non-medical masks most of the public is currently wearing. Researchers at Duke University put a variety of masks to the test to give a better idea of which face masks provide the best protection from COVID-19.
Researchers tested 14 commonly worn types of masks and a propylene face covering. They recorded the number of respiratory droplets transmitted through the masks while talking, and compared the results to the number of respiratory droplets transmitted unmasked. This helped them determine which COVID-19 face masks are best.
Researchers spoke into a black box with a green laser illuminating the inside, and a computer evaluated the number of respiratory droplets emitted. They spoke for 40 second intervals each. The first 10 seconds served as a “baseline” evaluation. The speaker then said “stay healthy, people,” five times during the next 10 seconds, and researchers observed the last 20 seconds. The experiment was repeated 10 times for each mask and for the control trial.
Researchers found “stark differences” in the masks’ effectiveness. N95 masks were the most effective, blocking over 99% of respiratory droplets. N95 masks are not recommended for public use, however, due to shortages negatively affecting the healthcare industry. Triple layered surgical masks were the second most effective, closely followed by double layered cotton masks.
Bandanas and neck gaiters “didn’t really work at all,” which was a surprise to researchers. Bandanas do not fit tightly around the chin, so a large proportion of respiratory droplets were able to escape. Researchers also found that neck gaiters “might make matters worse.” The gaiter appeared to make respiratory droplets smaller, which actually increases the risk of transmitting COVID-19.
Researchers did not test how coughing or sneezing could change efficacy. They also noted that the camera used may not have detected ultra-fine droplets.
The CDC recommends everyone over 2 years of age wear a mask that covers both the nose and mouth while in public. Cloth masks with a tight weave and two or three layers are recommended for additional protection. Many people in the medical field agree. Johns Hopkins University defines a safe mask as “a double layer of washable, breathable fabric that helps keep the wearer from spreading potentially infected droplets into the air.”
Business Insider suggests using a “candle test” to evaluate your mask’s effectiveness. If you can blow out a candle while wearing your face mask, it is likely too loosely woven to be effective against COVID-19. CNN suggests using a similar “light test” to evaluate the safety of your mask. If you hold your mask up to the light and can’t see the individual fibers, then your mask is tightly woven and more protective. If you hold your mask to the light and you can see individual threads, however, then your mask is likely less effective.
A polypropylene filter can also be added between cloth layers for an extra level of protection. Polypropylene, a common plastic, creates a static cling effect that traps outgoing and incoming respiratory droplets.
New strains of COVID-19 are spreading across multiple countries, more contagious and more deadly than the first. With the emergence of these strains in the U.S., some experts have recommended double-masking to better protect yourself. Not everyone believes double masking is more effective, however. A safe, multi-layered mask worn “consistently and appropriately” is more effective than double-masking, according to Johns Hopkins. Double masking could lead people to wear their masks incorrectly. The CDC still recommends wearing just one mask while in public.
Read more on coronavirus face coverings:
- Which protects you more from the coronavirus: A face mask or a face shield?
- Which U.S. states have mask mandates?
- Pandemic experts say we may live with masks for years
- Not all masks are effective against COVID-19: Here’s a ranking of how safe they are
- How face masks are affecting the deaf and hard of hearing community
- What’s the difference between an N95, an N99, and a R95 face mask?