“The way that the virus may be transmitted to others in this way is through contact – that is, if others inadvertently touch the soiled mask, and then their own face,” Wong said.

Leong Hoe Nam, an infectious diseases expert at Mount Elizabeth Novena Specialist Centre, said an exposed mask carries with it a “small risk” of passing a virus through the air.

“If exposed to the open, with strong winds, there is a small risk of aerosolisation,” he said.

Aerosolisation refers to a process where a substance such as one’s spit or mucus is dispersed and transmitted through the air.

“Either way, [improperly discarding used face masks] is disgusting and unhealthy,” he said.

The experts predicted the virus, when left exposed, could survive as long as a few hours to a few days.

Wong said that in Singapore’s hot, humid climate, the virus is likely to persist for no longer than two to three days, while Leong said the virus can survive “for hours” on an exposed surface.

Leong added that different germs can survive on a used mask for different durations. For example, bacteria can live for months to years if kept in a cool place, he said.

Fold, tie, wrap

Leong detailed several steps to take should one want to dispose of a used face mask, which he shared in Mandarin on a live-streamed Q&A session with Chinese daily newspaper Lianhe Zaobao recently.

He said that one should always wash their hands before taking off the mask, as touching one’s face with unwashed hands heightens the risk of illnesses.

After that, one should take off the mask, and fold it in half inwards, such that the droplets from the mouth and nose are not exposed. Then, fold the mask into another half, and then another half, until the mask looks like a roll. The mask can also be wrapped with its ear loops so that it will not unravel.

Then, Leong said the user should wrap the mask in a piece of tissue, before throwing it into a rubbish bin.

Associate Professor Alex Cook, Vice Dean of research at the Saw Swee Hock School of Public Health at the National University of Singapore, said people infected with a virus should be more mindful of where they discard their masks.

“If you are infected with a virus and are wearing a mask to prevent transmission – as you should – you can dispose of it in the regular bin,” Cook said. “But it would be a good idea to put it in a bag and throw it immediately in the trash rather than leave it sitting exposed.”

What if you want to reuse your mask?

In general, one should change face masks regularly, usually once its inner lining becomes moist, said Leong.

To reuse a face mask, Leong said that one has to keep it dry so that it can last as long as possible. One should take off the mask without pulling it under the chin so germs there will not attach to the mask.

“If dry, and the layers and shape are intact, I would consider putting it in a ziplock bag with a desiccating gel,” he said.

Desiccating gel is a substance that absorbs moisture and can keep a mask dry. If the mask is dry and not torn, it can be reused for two to three days.

Even when one is sick, he can still reuse the mask, provided the mask is not shared.

“No harm [reusing the mask]. Once you have been infected with a virus … It can’t reinfect you,” Leong said.