Health experts suggest stepping up protection against the highly contagious omicron variant with stronger masks such as N95s or KN95s.

It’s especially important now with health care systems under strain, and with people in higher-risk situations such as crowded, indoor settings for extended periods, says Linsey Marr, who studies viruses at Virginia Tech.

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The U.S. Centers for Disease Control and Prevention recently updated its guidance to recommend the kinds of masks used by health care workers, but also noted it’s important to pick a mask that fits well and that you’ll wear consistently.

“Our main message continues to be that any mask is better than no mask,” CDC spokeswoman Kristen Nordlund said in a statement.

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Previously, the CDC had said N95 masks should be reserved for health care workers because of supply shortages. There’s a special category of “surgical N95” masks that are generally not available for sale to the public that the CDC says should continued to be reserved for health care settings.

N95s have a tighter fit to your face than cloth masks and are made with a special material designed to block 95% of harmful particles. The fibers are pressed closer together than in cloth masks and have an electrostatic charge that attracts molecules to stick to the mask rather than passing through.

KN95s and KF94s offer a similar level of protection. A full list of masks that meet an international quality standard is available on the CDC website.

But be careful when buying. The counterfeit market is huge, and about 60% of KN95s in the U.S. are fake and do not meet quality standards, according to the CDC.

It’s hard to tell just by looking if a mask is counterfeit, so experts suggest buying directly from reputable sellers. Project N95 is also a known seller of valid brands, and Marr says she buys masks through industrial suppliers like Grainger or McMaster-Carr.

If you find certain N95s difficult to wear for long periods, experts suggest exploring the different shapes and styles available to see what works best for you.