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People taking health officials’ advice during the omicron surge to switch to N95, KN95 or KF94 masks are gaining more protection from the highly contagious variant — but unlike their old cloth masks, the higher-quality respirators can’t just be thrown in the washing machine.

The disposable masks are not necessarily single-use, but they can’t be reused for long periods of time. So how long can you wear one before you have to toss it and use a fresh one?

The short answer, according to experts: It depends.

There is no consensus for the general public on the number of times you can rewear an N95, KN95 or KF94 mask, but it’s not just guesswork. You should base your decision on a number of variables, experts say, including the mask’s condition, fit and integrity over time, and the circumstances under which you’ve been wearing it.

“It all depends on the duration, what type of setting you’re in and what you’re doing in that setting,” said Matt Carlson, safety officer for UCSF Health.

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Respirator masks are close-fitting masks that filter airborne particles very efficiently. They differ from surgical masks, which are looser-fitting and not meant for reuse.

N95 and KN95 respirators are so-named because they filter up to 95% of particles in the air. Respirators meet various international standards: N95 masks meet U.S. standards and are approved by the National Institute for Occupational Safety and Health; KN95 masks meet Chinese standards; KF95s offer 94% filtration efficacy and are basically the South Korean equivalent of an N95.

N95 masks have a cup, flat-fold or duckbill shape. KN95 masks are tent-shaped. KF94 masks are boat-shaped.

Consumers should be aware that counterfeit and subpar masks have been a problem since the beginning of the pandemic. The Centers for Disease Control and Prevention website offers guidance for identifying NIOSH-approved respirators.

No matter what kind of respirator you use, the more you wear it, the looser the elastic and seal around the face can become, according to Kirsten Bibbins-Domingo, vice dean for Population Health and Health Equity at UCSF.

Touching and removing the respirator also increases the chances of compromising its structural integrity, Carlson noted.

To judge whether your respirator is suitable for continued use, you should monitor its condition closely, Carlson said. He recommends checking regularly to determine whether the filter layers are visibly wet, soiled or dirty, or the outer edge no longer seals tightly around your face.

“If the respirator is not compromised, you can safely reuse it,” he said. When in doubt, you should toss it and rotate to a new one.

Again, there’s no hard and fast rule. But generally, Bibbins-Domingo said she doesn’t usually re-wear an N95 mask more than five times, and will toss it if it gets dirty or wet.

Some experts say the same respirator can be reused up to a week, if handled and stored properly. However, they say that if you wear it in a high-risk setting like a health care facility, it’s safest to discard it after a day.

To get the best use and protection from their masks, wearers should pay attention to how they handle and store them, experts say.

The CDC urges wearers to avoid touching the front of the mask at all, since your hands could contaminate your mask, or vice versa. Always remove the mask by its ear loops or head strap.

If you are out in public and need to remove your mask to, say, eat or drink, put it in your pocket, purse or a paper bag to keep it clean. Sanitize your hands after removing the mask. When you need to put it back on, make sure the same side is facing out, and wash your hands after putting it back on.

If you plan to reuse your respirator, the CDC recommends keeping it in a “dry breathable bag” such as a paper or mesh fabric one that will keep it clean between uses. Bibbins-Domingo said staffers at her hospital put their masks in individually labeled paper bags and hang them up after use.

Carlson advises people to rotate to a different respirator each day of the week, allowing the worn respirators to dry and stay clean in a paper bag or unsealed container.

Currently, there is no method for the public to sanitize respirators for reuse. When N95 respirators were in short supply early in the pandemic, the CDC established “crisis capacity” strategies for health care facilities, but noted that this is no longer necessary because respirator supply has increased significantly.

“There have been technologies shown to effectively de-contaminate disposable respirators, but those technologies are only available to healthcare organizations, and are only to be used in crisis situations,” Carlson said.

When your respirator reaches the end of the line, you should discard it — in the trash, not the recycling bin. The Environmental Protection Agency says that personal protective equipment, masks, included, can’t be recycled. They should be placed “securely” in a trash can — Marin Sanitary Service in the Bay Area recommends putting them in garbage bags — to ensure nobody else comes into contact with them.

Some environmental protection groups have urged people to cut the ear or head loops before tossing masks in the trash to prevent animals from getting caught in them, much like the advice to cut plastic soda rings.

Kellie Hwang is a San Francisco Chronicle staff writer. Email: kellie.hwang@sfchronicle.com Twitter: @KellieHwang

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