Masks are on sale on July 20, 2020 on a clothesline in the front yard of a house in Los Angeles.
Chris Delmas | AFP | Getty Images
According to an observational study published on Thursday in the medical journal Thorax, a homemade fabric mask may need two or three layers to effectively prevent the spread of the coronavirus.
Researchers at the University of New South Wales in Australia investigated the effectiveness of one- and two-layer, fabric coverings in reducing the spread of breath droplets that occur when an infected person speaks, coughs, or sneezes. They then compared these results with those of a three-layer surgical face mask.
The researchers used LED lighting and a high-speed camera to film the spread of airborne droplets created by a healthy person with no respiratory infection. The video for speaking was recorded at 850 frames per second, while coughing and sneezing were recorded at 1,000 frames per second due to the higher ejection speeds.
A three-layer surgical face mask was most effective in reducing airborne droplet distribution, the researchers found after reviewing the footage. The one-layer cover reduced the spread of droplets when speaking, although the two-layer cover better reduced the droplets by coughing and sneezing, according to the researchers.
"A fabric covering with at least two layers is preferable to a single layer," wrote Prateek Bahl from the Faculty of Mechanical and Manufacturing Engineering at UNSW, a lead author of the study, in the results. "Guidelines for self-made fabric masks should include several layers."
However, the researchers said that a single-layer face covering was better than no face covering at all. In addition, various other factors determine the effectiveness of cloth masks, such as the type of material, the number of layers, the arrangement of the different layers and the frequency of washing.
The single-layer face covering consisted of a folded piece of cotton T-shirt and hair ties. The two-layer cover was made using the sewing method shown by the Centers for Disease Control and Prevention. The researchers used tissue paper to simulate the nasal mucosa and cause a sneeze, according to the study.
The study comes when the Trump administration is pushing for the public to introduce face coverings to curb the spread of the coronavirus. According to Johns Hopkins University, the United States has the worst outbreak in the world with 4 million cases and at least 143,820 deaths.
President Donald Trump's response to the pandemic has also been increasingly examined. In recent weeks, Trump has downplayed the virus threat and has linked the surge in new cases to an increase in testing. Public health officials and infectious disease experts disagree with these claims, however, saying that the rate of cases that tested positive in the United States remains hospitalization and deaths high in some states.
Trump approved masks for the first time this week after struggling for months. The CDC began recommending face masks to the general public in April.
Earlier in the day, Adm. Brett Giroir, deputy minister of health at the Ministry of Health and Human Services, told reporters that 90% of the public or more must wear facewear to curb the spread of the virus.
"When we close the indoor bars, reduce restaurant occupancy, have facewear and hygiene, it's essentially tantamount to the shutdown of the entire economy, which means elective operations and everything else associated with them are shut down," said he.