WHO: Wear a Mask Indoors If Ventilation Is Poor

Public health officials around the world have been urging people to wear masks in public since the COVID-19 pandemic took hold this spring. Now, two major health agencies—the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC)—are taking the recommendations a step further.

Updated Guidance

Last week, the WHO released very specific guidance, urging people to wear masks indoors when ventilation in a building is poor. In its new guidance, the organization states that it is now recommending people wear masks when indoors "as part of a comprehensive package of prevention and control measures to limit the spread of SARS-CoV-2, the virus that causes COVID-19."

Just days later, the CDC released a new report also urging people to wear masks when they are inside. The report stated that the U.S. has entered a phase of “high-level transmission” of COVID-19 and urged people to wear masks at all times when they’re not home.

“The fact that the WHO and CDC are making these statements shows that there is a real risk,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Verywell. “People are letting their guards down in private gatherings and we’re seeing more transmission this way. If you wear masks in those situations, the risk will go down.”

WHO Guidance

The WHO’s new guidance is an update of the mask-wearing recommendations that were published in June. The WHO continues to recommend that healthcare workers wear masks at all times while working, but the organization’s advice for the general public is now more stringent than it had been in the past.

The WHO specifically recommends the following:

• People in decision-making positions should use a "risk-based approach" to decide on mask-wearing recommendations for the general public.
• In places that have known or suspected COVID-19 cases, people should wear non-medical masks inside as well as outdoors if they cannot maintain a 3.3-foot (1 meter) distance from others.
• Unless there is “adequate” ventilation, people should wear a non-medical mask indoors, “regardless of whether physical distancing of at least 1 meter can be maintained.”
• People with a higher risk of severe complications from COVID-19 (including those over 60 and people with underlying conditions such as cardiovascular disease or diabetes, chronic lung disease, cancer, cerebrovascular disease, or immunosuppression) should wear medical masks when they are not able to maintain physical distancing of at least 1 meter.

The WHO says that “a mask alone, even when it is used correctly, is insufficient to provide adequate protection or source control."

Hand hygiene, staying at least one meter apart from others, avoiding touching your face, and having “adequate ventilation in indoor settings” are also critical steps.

CDC Guidance

The CDC report says that “a multipronged approach to implementing all evidence-based public health strategies at both the individual and community levels is essential” to minimizing the spread of COVID-19.

While the CDC report covered several aspects of preventing the spread of COVID-19, it also featured new, detailed guidance on using face masks. The report states that “ compelling evidence now supports the benefits of cloth face masks for both source control (to protect others) and, to a lesser extent, protection of the wearer."

The CDC notes that using a mask consistently and correctly is "a public health strategy critical to reducing respiratory transmission” of the virus. This is especially crucial “in light of estimates that approximately one-half of new infections are transmitted by persons who have no symptoms.”

Face Mask Basics

The WHO released guidance on cloth face masks in June, which recommended that people wear a three-layer fabric face mask every time they go out in public where it is impossible to be socially distant.

The guidance specifically recommended that masks consist of:

• An inner layer of absorbent material (such as cotton)
• A middle layer to act as a filter or barrier (made of a non-woven material like polypropylene)
• An outer layer of a non-absorbent material (such as polyester or a polyester blend)

In its latest guidance, the WHO repeated these recommendations and stated that “Factory-made fabric masks should meet the minimum thresholds related to three essential parameters: filtration, breathability, and fit.”

What Experts Say

The WHO and CDC have technically already recommended people wear face masks when you’re around people from outside your household. However, Adalja points out that the latest guidance “is much more explicit.”

Adalja stresses that masks are not a perfect way of preventing the spread of COVID-19, but that they are still an “important tool” that can help, along with social distancing and good hand hygiene. “If you wear masks indoors, the risk of spread will go down,” Adalja says.

Peter Winkelstein, MD, executive director at the Institute for Healthcare Informatics at the University at Buffalo, agrees. "The new recommendations are absolutely warranted. If we're going to eradicate the pandemic, then we need to be much more consistent in our use of common-sense measures," Winkelstein tells Verywell. "And probably the most common-sense measure we've got now is face mask use. It works."

While many people have been wearing masks while shopping, Winkelstein says that they're "less careful" in office settings and around people they know. "You don't have that same 'stranger danger' sense. People kind of forget that even your friends, coworkers, and colleagues are potentially dangerous," Winkelstein says. "It's not their fault, but people can be contagious and not know it."

Winkelstein recommends that people keep a mask on whenever they're around people they don't live with.

Adalja is skeptical that people will start wearing masks indoors around friends and extended family. “Most people are not going to do this," he says. "People don’t think they’re at risk when they’re around people that they know, but the risk is always there.”

Winkelstein is hopeful that more people will start to increase their indoor mask usage. "Things are really bad. I have a lot of faith in people being sensible."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.