The cheap cloth masks can cause you more harm than good as researchers have found that wearing them may actually put people at higher risk of respiratory illness and viral infections.
The cloth masks' moisture retention, their reuse and poor filtration may explain the increased risk of infection, the study noted.
"Masks are especially important for frontline doctors and nurses, as their protection from infection is key to maintaining the ability to tackle a pandemic effectively," said lead study author professor Raina MacIntyre from the University of New South Wales, Australia.
"Cloth masks should not be used by workers in any healthcare setting, but particularly high-risk situations such as emergency departments, intensive care, paediatric or respiratory wards," MacIntyre noted.
For the randomised clinical trial (RCT) to study the efficacy of cloth masks, the researchers split 1,607 hospital healthcare workers across 14 hospitals in the Vietnamese capital, Hanoi, into three groups: those wearing medical masks, those wearing cloth masks and a control group based on usual practice, which included mask wearing.
Workers used the mask on every shift for four consecutive weeks. The study found respiratory infection was much higher among healthcare workers wearing cloth masks.
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The penetration of cloth masks by particles was almost 97 percent compared to medical masks with 44 percent.
Cloth masks remain widely used globally because they are a cheaper option especially in areas where there are shortages of protective equipment, including in Asian countries, as well as in West Africa, the study noted.
Professor MacIntyre said the study's results pointed to the effectiveness of medical masks, in addition to the harm caused by cloth masks.
The study was published in the journal BMJ Open.