Not all N95 respirator masks are created equal. In fact, you may unknowingly be wearing one that does more harm than good when it comes to preventing the spread of COVID-19.

That was the warning the San Francisco Department of Public Health sent via Twitter.

It said, in part, “the ones with the valves or openings on the front are NOT safe, and may actually propel your germs further.”

Getty Images

“Valves of that type permit droplet release from the mask, putting others at risk,” the order stated.

Experts who spoke with Healthline agreed.

“The virus can be transmitted through the valves, which offer no filtration at all,” said Dr. Ali Raja, executive vice chair of the department of emergency medicine at Massachusetts General Hospital and an associate professor at Harvard Medical School.

“Any mask with a one-way valve is only going to protect the person wearing it. It won’t protect anyone around that person from potential exposure to virus particles they exhale,” he told Healthline. “It may give the people surrounding them a false sense of security.”

“In the spirit of ‘your mask protects me and my mask protects you,’ a mask with a valve virtually makes that impossible,” said Jessica Malaty Rivera, MS, a microbiologist and contributor at the COVID Tracking Project.

“If you don’t have anything filtering what’s going out, it’s kind of like your mouth is an open air exhaust. And that’s the danger,” she told Healthline.