The World Health Organization recommends three layers of materials for fabric face coverings to provide the best protection.
For a nonmedical cloth mask, the WHO says in a new website post that there should be an inner layer of absorbent material such as cotton, a middle layer of nonwoven material for filtration such as polypropylene, and an outer layer of non-absorbent material such as polyester.
Dr. Maria Van Kerkhove, an epidemiologist and the WHO’s technical lead on COVID-19, said those layers in that order can “provide a mechanistic barrier” during a media briefing Friday, citing new research, Business Insider reported.
Health experts say fabric masks also should be worn correctly and cleaned. Contaminated hands can infect a person adjusting or frequently taking off and putting on a mask, said Dr. Tedros Adhanom Ghebreyesus, the WHO’s director-general.
“Current evidence suggests that most transmission of COVID19 is occurring from symptomatic people to others in close contact, when not wearing appropriate PPE [personal protective equipment],” WHO notes in its guidance. “There is also the possibility of transmission from people who are infected and shedding virus but have not yet developed symptoms … Some people infected with the COVID-19 virus do not ever develop any symptoms, although they can shed virus which may then be transmitted to others.”
The filtration of cloth fabrics and masks can vary greatly, ranging from 0.7% to 60%, says a WHO guidance, and the better the filtration the more protection a mask offers.
Fabric cloths, such as nylon blends or polyester, provide two to five times increased filtration when folded into two layers compared to a single layer. When folded into four layers, filtration effectiveness increases two to seven times.
WHO found that masks only made of cotton handkerchiefs with at least four layers only had a 13% filtration rate while masks made with very porous materials such as gauze only filtered out 3% of particles even with multiple layers.
Last week, the WHO expanded its recommendations for the use of face masks, advising people should wear fabric masks in places where social distancing isn’t possible such as in shops and on public transportation
Previously, the WHO had recommended that only health care workers, people infected with COVID-19 and their caregivers wear medical masks, taking into account the global supply shortage.
Earlier this year, the U.S. Centers for Disease Control and Prevention also altered its guidelines on face masks due to evidence that shows a “significant portion” of people with coronavirus who are asymptomatic or pre-symptomatic can transmit the virus through speaking, coughing or sneezing.
Due to that research, the CDC recommends wearing cloth face coverings in public areas where social distancing is difficult.
“If someone is sick, they may be less likely to spread infectious droplets if they are wearing a mask,” Dr. Amesh Adalja, a senior scholar for the Johns Hopkins Center for Health Security, told The Washington Times.
Health experts say masks should cover the nose and mouth and fit as closely to the cheeks as possible. People also should avoid touching the front of a mask and touching their eyes or mouth after removing a mask and wash their hands immediately afterward.
Masks should be stored in a sealable bag until they can be washed and cleaned, WHO says, so they don’t contaminate other surfaces. If the fabric layers look noticeably worn, masks should be thrown out.
“Remember, the use of a fabric mask alone is not sufficient to provide an adequate level of protection,” the WHO said in its guidance, adding individuals should still practice physical distancing and proper hand hygiene.
• This article is based in part on wire service reports.
• Shen Wu Tan can be reached at stan@washingtontimes.com.
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