In the coronavirus pandemic, masks are a sign of solidarity. But the effectiveness of homemade models is very different.
One of the notable developments in the coronavirus pandemic was how willingly many people took out their sewing machines, how lovingly and creatively they made covers for mouth and nose. And so you soon saw them everywhere: masks in all colors and shapes, from functional to funny. As a symbol of commitment and solidarity, they are undoubtedly an important contribution to the fight against the pandemic. However, it is less certain how effective such temporary solutions are. Several studies have now explored its effectiveness - and revealed significant differences.
According to a study from Great Britain, face coverings tested may do more harm than good. The researchers examined 14 different products. They let a person speak through all these barriers and measured how many droplets made it through - compared to speaking without covering. The cellulose-like surgical mask you can buy in the pharmacy held back at least 90 percent of the droplets. Various self-made coronavirus masks made of two layers of cotton caught around 80 percent. A bandana, on the other hand, let at least half of the droplets through.
And then came the surprise, according to author Martin Fischer of Duke University: "Common sense suggests that it's better to wear something on your face than nothing. But that wasn't the case here." When the speaker wore a fleece covering - a tube scarf pulled over the face, as athletes like to use it - more droplets came out in the end than when speaking freely. The researchers suspect that the material finely atomized the droplets. This could make the product counterproductive because smaller droplets stay longer and can fly farther than larger ones and warn the authors.
Coronavirus masks with two layers of different materials did very well
The study is only small; it is questionable whether the findings can be generalized. Nevertheless, the findings fit with other works that have shown that not all corona virus masks are the same. For example, a US team tested various materials using an apparatus that produced particles. There were also downward outliers: a layer of coarsely woven cotton, for example, only held back around ten percent of the small particles. According to the study, masks that combined a layer of cotton with another made of silk, chiffon, or flannel offered particularly reliable protection. As the different substances rub against each other, they become electrostatically charged, thus attracting the particles and increasing the chance that they will get stuck in the mask, so the explanation.
Alternative solutions are not only relevant for people queuing at the supermarket checkout. In the healthcare industry, masks were sometimes so scarce that US researchers recently saw the need to test emergency solutions for professional use: N95 masks whose expiration date had expired more than ten years ago, and sterilized and reused products were among them.
Surgical masks must be tied tightly around the head. Otherwise there is little self-protection
N95 masks get their name because they capture at least 95 percent of all particles from the ambient air. They, therefore, also protect their carriers and are especially important for medical employees who come into contact with potentially infected people. In the current test, the products commonly used in the USA easily managed 95 percent - even if they were treated with disinfectants or heat or had expired years ago. Surgical masks protected the wearer from around 75 percent of the droplets when they were tied tightly around the head with ribbons. On the other hand, if these masks were attached behind the ears with a non-adjustable elastic band, they only stopped 38 percent of the small particles.
What do these values mean now? First of all, it is a very complex undertaking to assess the face masks' effectiveness reliably. Droplet size, material, the distance to other people, and environmental factors play a role. In addition, the routes of infection from Sars-CoV-2 are still not fully understood.
Nevertheless, the experience in countries that have introduced masks suggests that mouth and nose protection is definitely useful, even if its effectiveness does not reach perfect values. Suppose the masks filter the majority of the particles. In that case, this may be enough to prevent disease in most cases, wrote the infection specialists Caitlin Dugdale and Rochelle Walensky in the journal Jama Internal Medicine. And in the end, it is probably not the laboratory measurement that is decisive anyway, but the fact of how reliably people use face protection. In other words: even an improvised covering that sits firmly on the face is usually more useful than a tip-top-tested mask that hangs under the chin.