In recent months, there’s been a surge of interest in materials laced with the copper, including bed sheets, socks, and coatings that can be sprayed onto surfaces. Multiple companies, too, are marketing face masks with built-in copper linings, touting their germ-killing properties.

But while copper does have antimicrobial qualities, some experts say you should think twice before using it. Earlier this week, a signage posted on Makati Medical Center caught the attention of the public. One of its doctors, Angelo Lozada, posted on social media the advisory that prohibited the use of copper masks, as well as those with valves, in the hospital's premises.

Turns out, these masks can promote the spread of the virus. “The copper masks have that ‘hole’ at the bottom chin area. I’m presuming it’s because of that," Lozada wrote, responding to one netizen.

In a statement released yesterday, Makati Medical Center said that its Infection Prevention and Control Department "reiterates that to all patients, visitors, healthcare workers, employees, and outsourced service providers that masks with exhalation valves, vents, slits, or holes are not allowed."

And still, according to reports, not all metal-infused masks are created equal. Manufacturers would need to design them with enough copper—ideally near the product’s surface—to actually do the job. Individuals, therefore, are still advised to put on a surgical mask for their own protection.