Demand for face masks has been outstripping supply in Japan ever since the ‘state of emergency’ was declared on April 7th. Do they really work? Guidance on face masks varies wildly. The World Health Organization (WHO) currently only recommends face masks for people who are coughing or sneezing, or for those who are caring for people who are thought to have COVID-19.

But in Lombardy, the worst-hit region of Italy, face masks are mandatory, and as of 3 April, the US Centers for Disease Control and Prevention recommend that people wear a “cloth face covering” whenever they go outside.

With a worldwide shortage of face masks, limited supplies are being reserved for healthcare workers. That leaves the rest of us with a dilemma: do we wash and reuse the masks we have, or make our own?

Plenty of enterprising folks are opting to make their own masks, but few can match the mask belonging to Twitter user SiNN (@SiNN927). "My mother made me the strongest mask. She’s a real pro when it comes to sewing,” he Tweeted.

SiNN’s mum was inspired by the popular American comic "Ninja Slayer." A ninsatsu menpo is a special mask worn by the titular character who swears to kill ninjas. It has the word ninsatsu, written with the kanji 忍 (stealth) and 殺 (kill) embroidered in white.

As soon as SiNN’s mum gave him his new mask, he rushed to try it on. He took this picture, which he posted on Twitter. “This is definitely strong! It’s really well made,” he Tweeted.

SiNN’s ‘strongest mask’ soon became a hit on Twitter. Many users responded to SiNN’s picture, commenting on its good quality and striking design.

“What kind of mask is that?” asked one.

“I want one!” enthused another.

“That’s too cool!” wrote another.

How do you make a face mask? It certainly doesn’t do any harm to add some words of defiance. Wearing a mask that makes you feel like you've been possessed by the spirit of a powerful ninja won’t make your immune system stronger, but it will do your confidence a world of good!

Medical experts say that an effective mask is one that fits well around the nose, mouth, and chin, and doesn’t let air in around the sides. According to a 2013 study that compared various household materials based on their ability to filter out viruses and bacteria, tea towels are pretty effective, but your best bet is to refashion a vacuum cleaner bag.