Face masks are now a regular item in the new normal to protect wearers from COVID-19. Recently, scientists presented the quantitative protection levels of various face masks, including those made from common fabrics. Their evidence was included in the revised guidelines of the World Health Organization of the United Nations.
The quantitative values of face masks in protecting people from COVID-19 were presented by scientists at Stanford University, a private research university. Their findings suggested that face masks made of common fabrics have a filtration efficiency rate of between 5% and 20%. While face masks made of paper-based materials had a rate of between 10% and 20%. These percentages indicated that wearing any kind of face mask could offer protection, compared to not wearing any at all. The results were published in journal Nanotechnology Letters.
The New Guidelines for Face Masks in COVID-19 Pandemic
SARS-CoV-2, the virus that causes COVID-19, is more often transmitted through respiratory droplets when an infected person coughs or sneezes. These droplets can be emitted through both means at an incredible speed, making it difficult for someone unprotected to dodge. As such, governments and health departments advise the public to wear face masks or face shields, but face masks have higher availability than face shields. So, even fabric-based face masks are allowed to be used in public.
According to the updated guidelines from the World Health Organization (WHO), medical or surgical face masks are recommended for select groups, such as healthcare workers, people with mild symptoms of COVID-19, non-healthcare workers who are caring for those who may have COVID-19, people who have a higher risk of being infected, and people who cannot maintain social distancing due to valid reasons. Moreover, people who have underlying health conditions, and those aged 60 and older are advised to wear medical masks if possible.
For non-medical grade fabric face masks, the WHO agrees with using them in public. However, the organization does not recommend them in controlling the disease. This is because of the limited evidence on the effectiveness of fabric face masks. Though, the WHO encourages the use of these items for the general public and in cities with limited capacity for implementing control measures. Thus, numerous people around the world use fabric masks to comply with community quarantine protocols.
Regardless of limited evidence against COVID-19, the organization supports the wearing of fabric masks but warns about potential risks. The main benefit of these masks is to provide a barrier to limit the transmission of liquid droplets. The main drawback, on the other hand, is the effect of face masks on breathing, especially in an extended period. So, when going outside and cannot find a medical mask, wear a fabric mask, never touch one's face, and wash hands as soon as possible. At home, face masks are not needed if no one has COVID-19, has respiratory symptoms, and has an underlying medical condition like cancer.
The Filtration Efficiency of Different Face Masks
At Stanford University, scientists detailed their recent study on the filtration rates of various face masks used to fight the pandemic. Their findings were utilized in the revised guidelines by the WHO. While fabric masks were not on par of medical masks, they provided a significant level of protection than not wearing a mask. Their quantitative measures would be significant in prioritizing groups that should receive medical masks in clinical and public settings.
"Many people argue that cloth masks can't be effective because they can't filter out viral particles, which are extremely tiny… Most of these particles leave the mouth and nose in much larger droplets that become smaller through evaporation as they move away from the body. Trapping droplets with the mask means not nearly as many viral particles escape. So, when all parties in a gathering are wearing well-constructed, well-fitting masks, it provides an extra layer of safety for everyone," explained Dr. Amy Price, a senior scientist from the Anesthesia Informatics and Laboratory at Stanford.
In the study, the masks were divided into two main categories: personal protection materials and household materials. Personal protection materials included N95 respirators and medical face masks, while household materials comprised fabric masks, clothes, paper products, and tissue paper. All of these items were tested in filtering respiratory droplets, which could contain coronaviruses and other pathogens. Then, they compared the filtration efficiency of each item to show the effectiveness in COVID-19. The same comparison also highlighted if an item was useless against the disease.
The comparison showed that each item offered some level of protection, and not one was found to be entirely useless. In the initial filtration efficiency rates, the N95 respirators had the highest performance at 95.94% in personal protection materials. That rating shows the true efficiency of N95 in blocking particles of 0.3 microns in size or larger. Medical-grade face masks offered filtration efficiency rates of between 18.81% and 33.06% depending on how they were manufactured.
Among household materials, sweaters had the highest initial efficiency rates at 25.88% in the clothing subcategory. It was followed by exercise pants at 23.33%, t-shirts at 21.62%, and toddler wrap at 17.5%. Other clothes had efficiency rates of less than 10%. For the cellulose subcategory, copy paper had the highest rate of 99.85%, even greater than N95 respirators. It was followed by tissue paper at 20.2% and paper towels at 10.41%. While copy paper scored nearly 100%, breathing through the material could be very difficult.
When real-life conditions were applied, the efficiency rates of the materials changed dramatically. Conditions like temperature and pressure had influenced the ability of the items to block respiratory droplets. Overall, N95 respirators remained with the highest filtration efficiency rate of 95% or greater while allowing the wearer to breathe. Cotton and polyester face masks without visible pores or which consisted of multilayer configurations could offer up to 20% filtration. Paper towels and tissue paper could provide up to 20% filtration, but were better used as a composite material for certain masks due to low mechanical strength.
Meanwhile, nylon could provide 20% filtration if conditions were met. Pressure could substantially alter its performance in blocking respiratory droplets. Scientists recommended a lower pressure drop in using nylon as material for face masks. Silk had the lowest filtration rate of 5%, though, considered useful if cotton and polyester were unavailable.
The values presented by the research team empower the use of fabric face masks in public. The details also offer insights into those who are planning to create their own masks for personal use or for their business.