Since the coronavirus pandemic was declared back in March, the benefit of wearing a face mask has been one of the most highly debated topics.
In England, face masks are currently compulsory on public transport as well as in several indoor settings, including shops, supermarkets and museums.
Face masks come in a range of forms, including surgical masks, cloth coverings and masks with valves.
Now, the Centres for Disease Control and Prevention have urged people to avoid masks with valves.
It explained: “The purpose of masks is to keep respiratory droplets from reaching others to aid with source control.
“However, masks with one-way valves or vents allow air to be exhaled through a hole in the material, which can result in expelled respiratory droplets that can reach others.
“This type of mask does not prevent the person wearing the mask from transmitting COVID-19 to others.
“Therefore, CDC does not recommend using masks for source control if they have an exhalation valve or vent.”
The warning comes shortly after experts from the University of New South Wales in Sydney wanted that homemade face coverings need to be at least two layers and preferably three to curb the spread of Covid-19.
The team found that one layer of cotton T-shirt material is fairly effective as a barrier against droplets expelled during speaking, but two are "significantly better at reducing the droplet spread caused by coughing and sneezing".
