Besides profiteering and online scams, people searching for masks have another problem to worry about - substandard or fake ones.

One customer, who wanted to be known only as Mr Wee, told The New Paper that he was unable to find masks in pharmacies for over a week. He finally found some at a pop-up store in Lucky Plaza on Feb 4.

Mr Wee, 46, bought one box of 50 pieces for $17. While most pharmacies limit one box a customer, buyers there could purchase any number of boxes.

Mr Wee grew suspicious when he realised the box had no brand nor address.

He said: "The masks looked thin compared with the other masks I had. The filter layer is very porous, while the masks I bought from pharmacies had a thicker middle ply."

He said there were some other stores in Lucky Plaza selling masks that looked dubious, such as individual packets of masks without boxes.

In another case, student Stan Kee, 18, said his aunt had unknowingly bought for him substandard masks from Johor Baru in Malaysia.

Mr Kee said: "They went to JB because so many masks were sold out or too expensive in Singapore. In JB, it is around $10 for 50 pieces."

But while the box indicated the masks were three-ply, Mr Kee found that they were single ply and flimsier than usual.

Much like Mr Wee's case, the masks were without a brand.

In China, the authorities have cracked down on fake medical supplies and seized 31 million fake or substandard face masks.

Online retailer Shopee has also taken action against fake or misleading products listed on its website, including masks.

A Shopee spokesman told TNP: "Shopee does not tolerate the listing of fake or misleading products and has in place robust measures, including both manual and automated screening processes, to prevent and remove such listings."

TNP has contacted the Health Sciences Authority for comment.

Dr Leong Hoe Nam, an infectious disease specialist, said sellers are preying on fear.

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He said effective masks need three components: a metal piece to secure the mask to the nose, a close fit to the face with ear hooks or a ribbon, and a filter layer.

Regarding the rising trend of homemade masks, Dr Leong said having a mask is better than no mask at all.

He said: "But it depends on how tightly fitted the mask is to the face. The problem with a cloth mask is if it doesn't have the metal piece, the material used may also not be effective.

"These masks come in different shapes and sizes, so it is hard to endorse."