5 Questions: Stanford scientists on COVID-19 mask guidelines

Scientists say we should wear masks to control the spread of COVID-19. Stanford experts share the evidence that informed the World Health Organization’s recommendations.To get more news about nonmedical dust proof mask, you can visit tnkme.com official website.

On June 5, the World Health Organization revised its guidelines about when people should wear cloth masks. Previously, the organization had recommended that only those with symptoms of COVID-19, the respiratory disease caused by the novel coronavirus, or those caring for them, wear cloth masks over the nose and mouth.

The new guidelines recommend that everyone who comes in close contact with others in crowded or close quarters, such as on a bus or in a store, wear a cloth mask composed of at least three different layers of material. People 60 or older, or those with underlying health conditions, should wear medical masks, such as surgical masks, in public, and physicians and health care providers should wear medical masks in all areas of a hospital, even if the area in which they are working has no COVID-19 patients, according to the organization.

The new guidelines were devised after WHO officials reviewed information from researchers at Stanford and elsewhere about the ability of cloth masks to slow the spread of the disease, which has now infected more than 8 million people worldwide and caused more than 400,000 deaths.

The revised recommendations more closely echo those of the U.S. Centers for Disease Control and Prevention, which since early April has recommended cloth masks in public settings where social distancing is difficult to maintain.

Science writer Krista Conger spoke with two Stanford researchers involved in the change to the WHO guidelines: Amy Price, PhD, a senior research scientist at Stanford’s Anesthesia Informatics and Media Laboratory, and Larry Chu, MD, a professor of anesthesia and director of the AIM Laboratory. They recently co-authored an article in Nanotechnology Letters assessing the filtering and breathability of various household fabrics often used to make masks.
1. How do cloth face coverings prevent the spread of COVID-19?
Chu: In order to answer this, it’s first important to understand the concept of source control. We’ve learned that as many as 40% of people infected with the virus that causes COVID-19 may have no symptoms. But when they talk, cough or sneeze, they can still spread the virus to others in the form of respiratory droplets expelled into the air. Those droplets evaporate into fine particles that may linger. The mask traps these larger droplets before they can evaporate. So, wearing a mask regularly can prevent spreading at the source even when we don’t know we are sick. But masks are just one important way to prevent this disease from spreading. Washing your hands regularly and thoroughly and keeping at least 6 feet apart from one another are still vitally important.

Price: Many people argue that cloth masks can’t be effective because they can’t filter out viral particles, which are extremely tiny. But, as Larry explained, 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. If two people are wearing masks, the viral particles can travel about 5 feet away from each individual. When an infected person is not wearing a mask, those particles can floatthrough the air 30 feet or more and stay alive for up to 30 hours.

2. How do you respond to people who feel that wearing a mask can be harmful?
Price: I’ve heard so many misconceptions about cloth masks. Some people think that if you wear a mask for long periods of time you will trap and breathe in excess amounts of carbon dioxide, which could lead to brain damage. That’s just not true. A properly constructed mask provides more than enough ventilation. In fact, one way to test if your mask is well made is to try to blow out a candle through the mask from about 1 foot away. If you can’t do so, your mask might be too tightly woven. Other people feel that wearing a mask encourages people to touch their face and to loosen their adherence to other safety precautions like social distancing and hand washing. We’ve found the opposite. Wearing a mask reminds people to continue to be cautious. With a mask on, you actually touch your face less. People who experience skin irritation should ensure their mask has a layer of wicking fabric, like cotton, against the face, and everyone should change the mask if it becomes wet or dirty. Finally, it’s been suggested that mask-wearing may increase the concentration of viral particles around an infected person’s mouth and could increase the severity of the illness. While it’s true that some studies of health care workers have suggested that the viral dose is an important determinant of infection, it’s different for someone who is already infected. If you are sick, you already have the virus in your lungs; it’s not going to get any worse.

3. What’s the best way to make and use a mask?
Chu: Our studies show that, if constructed properly with high-quality materials, a homemade cloth mask can function as well as or better than a surgical mask. Based on our studies, the WHO now recommends a cloth mask of at least three layers of different materials. The outermost layer should be made of a fabric that is at least somewhat water resistant. That can be a fabric that is a combination of cotton and polyester, nylon or rayon. The middle layer should either be a polypropylene — a spunbond material used in some reusable grocery bags, mattress covers and craft projects — or three-ply disposable facial tissues like Kleenex. Finally, the innermost layer should be a wicking material to draw moisture away from the face. One hundred percent soft cotton works well here.