Mask wearing in public is considered essential to reduce the spread of the coronavirus.

Masks are flying off the shelves, they are hawked on the streets and people are improvising and making their own because they can’t afford better ones.

We all know the bra mask – one brassiere makes two – doesn’t work.

But there are also others that are literally useless and ineffective because they are improperly made or unsuitable.

It is assumed that wearing masks reduces the likelihood of an infected person spreading the virus and the likelihood of a properly masked person inhaling droplets containing the virus.

Then there’ the problem of aerosol transmission of tiny virus-laden particles that linger in the air after an infected person has passed.

Health experts have warned that users should beware.

In a study published in the ‘Science Advances Journal’ on Friday, health experts tested 14 commonly available masks. They included the professionally fitted N95 respirator mask, usually reserved for health care workers.

The N95 came out on top, followed by the three-layered surgical mask.

Some homemade cotton masks also proved to be fairly effective in controlling the transmission of droplets. The popular African-print masks are not as effective as others but better than none at all, the Ministry of Health says.

Industrialization CS Betty Maina has said masks of woven cloth don’t protect from Covid-19.

“It may protect you against dust and other particles in the air but it will not protect you against this disease n because it does not have an inner filter,” she said.

The worst – literally useless – is the neck fleece or gaiter designed for runners and other sportsmen. It keeps the neck warm and its many folds can be pulled up over the face. It’s not designed to keep out droplets.

The goal of the analysis was to compare the efficacy of different masks by estimating the total transmitted droplet count.

Researchers from the physics department of Duke University in North Carolina in the US demonstrated a simple method using a laser beam and cell phone to evaluate the efficiency of masks.

It measures the transmission of respiratory droplets during regular speech.

“Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive,” the study says.

In fact, wearing a fleece mask resulted in a higher number of respiratory droplets because the material seemed to break down larger droplets into smaller particles that are more easily carried away with air.

Folded bandanas and knitted masks also performed poorly and offered little protection.

The study said: “Shortages in supply for surgical face masks and N95 respirators, as well as concerns about their side effects and the discomfort of prolonged use, have led to public use of a variety of solutions. [These] are generally less restrictive such as homemade cotton masks or bandanas, but usually of unknown efficacy.”

The Kenya Bureau of Standards has threatened to arrest hawkers selling cloth masks, saying it has not approved them because studies have shown they are useless.

Kebs said bogus products give unsuspecting users a false sense of protection while increasing the risk of exposure.

Managing director Bernard Njiraini said an effective mask must factor in the filtration capacity, efficiency of the material, capacity to absorb moisture and the fit of the mask to the wearer’s face.

“This [wearing substandard masks] not only compromises the efforts to contain the virus, not to mention other harmful effects that may arise from using substandard products,” Njiraini said.

Prof Ruth Nduati from the University of Nairobi said proper masks are effective when people are infectious even before they have symptoms and for the infectious asymptomatic cases.

Since the situation has evolved to community transmission, more people should wear masks, she said.

“ …wearing a mask will make a difference as there are other people we can’t identify because they are asymptomatic,” she said.

An earlier study by Cambridge and Greenwich universities said that when lockdowns are combined with 100 percent face mask use, disease spread is vastly diminished.

It can be reduced by as much as 18 months, the study estimated – the time frame frequently cited for developing vaccines.