Masks save lives: Here's what you need to know

Aug 30, 2023

Harvard Health Blog

Surging COVID-19 rates throughout the country and in many parts of the world make our efforts to protect ourselves and others more important than ever. Layers of protection offer the best defense against COVID-19, starting with vaccines and boosters for everyone eligible.

Vaccinated and boosted people are far better protected against severe disease, hospitalizations, and death. But everyone — even vaccinated people — may spread infection with a highly contagious variant like Omicron if they get it. In places where vaccination rates are low or COVID cases are rising, experts estimate we can save thousands of lives and help control the pandemic if we all commit to following mask guidelines and other standard preventive measures.

An expanding body of evidence supports the benefits of medical and nonmedical masks. Some of the strongest evidence includes these reviews (here and here) and observational studies (here, here, here, and here), which found that mask-wearing leads to lower rates of infection. And this impressive graphic display from the New York Times shows how masks help trap larger respiratory droplets and some of the smaller particles known as aerosols.

Mask-wearing helps protect against illness from viruses that travel through the air — not just COVID-19, but also colds and flu. Some people worry that masks trap carbon dioxide (CO2) or limit the amount of oxygen you inhale, but that's not true. As you breathe out in a mask, C02 escapes; as you breathe in, you receive oxygen.

No single study is perfect or definitive; in fact, such studies would be impossible to perform. But there is a lot going for mask-wearing, and little or no evidence that wearing a mask causes harm.

The Centers for Disease Control and Prevention (CDC) recommends wearing the most protective mask you can find.

Consistently wearing masks designed to filter out very small particles offers the best protection against highly contagious variants, such as Omicron. Examples include

Unfortunately, counterfeit N95 and KN95 masks have become common. The CDC offers useful information on ways to spot counterfeit masks.

Surgical masks are helpful, but less protective, partly because they do not fit snugly. Some experts suggest double-masking if you're using surgical or cloth masks.

What about tightly woven cloth masks with a wire bridge and at least two layers of washable, breathable fabric that completely cover the nose and mouth? These masks can be comfortable but offer less protection than N95 and KN95 masks.

Gaiters and bandanas may offer little protection and aren't generally the first choice, because they were not designed to provide tight facial coverage and may have only one layer. Masks with vents or valves are also discouraged, as virus particles can more easily escape through them.

Here are a few of the most common and important questions for which we don't have great answers just yet.

Masks work well only if worn consistently and correctly.

The CDC offers advice for

The best available evidence shows that mask-wearing can help reduce spread of COVID-19 infections, keep waves of serious illness from overburdening our hospitals, and save lives — possibly even yours.

Follow me on Twitter @RobShmerling

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

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