Why masks with breathing valves don't stop spread of new coronavirus

Corrections & Clarifications: A previous version of this article incorrectly spelled the name of Dr. Kristine Romine.

Masks mandates are in place in cities across Arizona, and these mandates are increasingly banning the use of masks that have valves. 

Though these one-way valves are designed to help provide more comfort by allowing air to escape the mask when users exhale, that function also allows the virus to spread.

"It defeats the purpose," said Kai Singbartl, a medical doctor who serves as the chair for infection prevention and control at the Mayo Clinic in Arizona. "They are unfiltered, those valves are the path of least resistance so to speak, it's easier to exhale and get rid of the heat and moisture."

But, in addition to exhaling heat and moisture, Singbartl said wearers are exhaling viral droplets and particles as well. Because of this, Maricopa County has specified in their mask mandate that valve masks do not comply with the county's masking requirements.

In an email, a spokesperson for Maricopa County wrote that the county's ban was based on a Centers for Disease Control and Prevention recommendation against the use of valve masks in health care settings.

Yuma, Pima and Santa Cruz counties all have mask requirements with similar specifications against valve masks.

However, other county mask mandates, such as Coconino County's, do not have specific restrictions against the use of valve masks, and those that do have bans against valve masks don't always seem to be enforcing them.

Mayo Clinic isn't allowing patients inside if they are wearing valve masks, but Singbartl said he has seen people wearing them before they are asked to put on a different type of mask. He said he has even seen health care professionals who don't work at Mayo Clinic using these types of masks.

"In a sterile field they're absolutely banned because it allows unfiltered, exhaled air in," said Kristine Romine, a doctor at Camelback Dermatology & Skin Surgery, where they are also not allowing in patients who are wearing valve masks.

A Maricopa County spokesperson wrote in an email that Maricopa County Public Health is "not an enforcement agency" and said if there are unresolved issues between individuals or businesses, they are encouraged to contact their local law enforcement nonemergency number.

Additionally, they recommended further education about the masks.

Romine has also seen some people wearing valve masks in public and thinks that people who are wearing the masks may not even realize that they may be further spreading the virus through the mask, since these masks are often available online for purchase and marketed as effective filtering devices.

"When you look at it, you think, wow this should be really protective," she said. "But it does not decrease the transmission of COVID-19 and you're supposed to protect both the wearer and the person six feet away."

Mask policies continue to evolve and shift as researchers learn more about the virus, but for now, Singbartl recommends using masks that cover both the nose and the mouth with some sort of material such as cotton cloth and to ensure that masks fit snugly on the face to prevent virus particles from escaping or entering.

"In general, the more layers, the better," he said. "Another important factor is thread count."

Higher thread count fabrics serve as more efficient filters, according to Singbartl. Since different materials may interact with the virus differently, he also recommended combining different materials together in one mask, such as silk and cotton, so that masks can filter out a broader range of particles.

He said he wants to see masks become mandatory statewide, with a provision against valve masks as well.

"It's really about protecting others," he said. "If we want to get back to somewhat of a normal life, we will be able to interact much more normally if we have masking requirements."

Amanda Morris covers all things bioscience, which includes health care, technology, new research and the environment. Send her tips, story ideas, or dog memes at amorris@gannett.com and follow her on Twitter @amandamomorris for the latest bioscience updates.

Support local journalism. Subscribe to azcentral.com today.