The Aga Khan University Hospital has banned the use of masks with valve respirators within its premises with immediate effect.
Masks are now commonplace across the globe as experts advise face coverings can help cut the spread of coronavirus.
However, scientists have warned not all facial coverings protect both the wearer and those around them.
Thus, the hospital in a statement on Wednesday warned such masks only protect the wearer and offer no protection to those around them.
“The design of these masks allows inhaled air to be filtered but the exhaled air is not. The exhaled air can be expelled towards others even more than from a person not wearing a mask,” the hospital’s statement read in part.
“Some types of masks, including N95 masks as well as cloth masks, include a plastic one-way valve on the front that makes it easier to breathe.”
“When you breathe in, the valve is closed, but when you breathe out, it opens to allow your exhalation to leave unfiltered.”
The World Health Organization (WHO) does not advise using masks or respirators with exhalation valves.
However, recent studies have found that they are less effective at preventing the spread of the coronavirus because they put people near the wearer at risk.
In April, the government published a law which imposed a fine of Sh20,000 and a jail term of six months, or both, for anyone found not wearing a mask in public as a preventative measure against the spread of the Coronavirus pandemic.
The law also requires the mandatory use of face masks in public vehicles as well.