During the pandemic, the FDA has granted emergency-use orders to allow millions of N95 and KN95 face masks to be imported from around the world to help combat a dire shortage of protective equipment in the US.

But, according to a report published online September 22, as many as 60-70 percent of those masks imported to the US from China may not meet America's minimum safety standards.

Researchers at ECRI, an independent nonprofit researching safety and cost-effectiveness in healthcare, tested nearly 200 KN95 masks from 15 different manufacturers.

They found that a significant majority filtered out fewer than 95 percent of particles, a standard the helps protect healthcare workers and first responders from possible coronavirus infection.

That could indicate that of the hundreds of thousands of masks imported from China during the pandemic, up to 70 percent may be less protective than advertised, the study said.

"We're finding that many aren't safe and effective against the spread of COVID-19," Dr. Marcus Schabacker, president and CEO of ECRI, said in a press release. "Using masks that don't meet US standards puts patients and frontline healthcare workers at risk of infection."

The study follows another that found that as many as 60 percent of imported N95 and KN95 style masks failed minimum safety requirements, according to testing by the US National Institute for Occupational Safety and Health (NIOSH), which sets the standards.

The Centres for Disease Control and Prevention (CDC) is aware of the issues with some imported masks, and have released a guide to spotting subpar products that may be misrepresented as meeting US standards.

Faulty face coverings may still offer better protection than some cloth masks

Even sub-standard masks offer better protection than poorly-constructed DIY cloth masks or nothing at all, experts say.

However, a quality seal is crucial.

Masks that have head and neck straps provide more protection than those with ear loops, according to ECRI, since they create a tighter seal on the user's face. KN95 masks, which are designed to Chinese standards that different slightly from NIOSH's, often have ear loops.

For people who are treating or exposed to someone who has COVID-19, masks that aren't certified at 95 percent particle filtration should be used only as a last resort.

"KN95 masks that don't meet US regulatory standards still generally provide more respiratory protection than surgical or cloth masks and can be used in certain clinical settings," Michael Argentieri, vice president for technology and safety at ECRI, said in the press release.

"Hospitals and staff who treat suspected COVID-19 patients should be aware that imported masks may not meet current US regulatory standards despite marketing that says otherwise."

In some cases, US healthcare workers are managing the shortage of certified masks by reusing (sterilized) N95 respirators, or using respirators that have expired. Research suggests these may be better protection than alternatives, including surgical masks.

This article was originally published by Business Insider.

More from Business Insider: