Masks are very effective at preventing respiratory droplets coming out of the wearer’s nose and mouth. Masks provide protection for the wearer too, reducing our exposure to droplets that may contain the virus that causes COVID-19.
Confused about masks? You’re not alone. There have been many confusing and inaccurate messages about masks circulating in the news and media. Early on in the US, we made the mistake of not recommending masks. Now we know better: the scientific evidence overwhelmingly shows that masks and face coverings protect others and ourselves from COVID-19.
- Why masks are helpful.
- What types of masks and materials are effective.
- How to wear and care for masks.
- How to maximize protection with masks, including double-masking.
- Frequently asked questions
Why are masks helpful?
1. People without symptoms spread COVID-19.
Studies show that almost half of all people with COVID-19 don’t have symptoms at the time of transmission. When we’re around a group of people, we won’t know who has COVID-19 and who doesn’t. The only way to prevent spread is for all of us to wear masks and maintain 6 feet or more distance when around other people indoors and outdoors.
2. COVID-19 is transmitted by respiratory droplets, which masks block.
The virus lives in droplets that come out of our noses and mouths. When we talk, these droplets travel 6 feet. When we cough or sneeze, the droplets can travel up to 30 feet. Yuck! Luckily for us, face masks are effective at blocking these droplets.
3. Wearing masks protect others and ourselves from COVID-19.
What type of masks and materials are effective?
The most effective mask is the one that you will wear!
Finding a mask that is comfortable enough to keep your nose and mouth covered without needing to frequently adjust and touch it is the most important thing to look for in a mask.
If you can and want to choose based on potential efficacy: the better the covering fits around the nose, chin and cheeks without gaps, the better it blocks.
Style/fit: Sewn cloth masks with ear loops or ties that go around the head block better than bandanas, gaiters and scarves that are looser.
Wearing and caring for masks:
- Wash or sterilize reusable masks and coverings before first use.
- To wash reusable masks, use the hottest water and drier setting that is safe for the material. Coverings can also be washed in hot water and dried in bright sunlight for disinfection. To sterilize, boil in water for 10 minutes.
- Wash or sanitize your hands before and after you put the mask on.
- Take masks off using the ear loops or straps and avoid touching the outside surface before you put it in the wash.
- Wash reusable masks or coverings or discard disposable ones after one trip out in the community.
If you need to reuse a disposable mask because you don’t have other options, only do so if it hasn’t gotten wet, dirty or torn. If you must reuse a disposable mask, let it dry completely between uses, at least a full day…and better if it dries for 3 days or more. That gives enough time for potentially infected droplets to dry and die. Don’t wipe it down or make it wet because it disrupts its droplet repellent properties.
Instructions to make your own masks:
- CDC: easy no-sew designs and sewn designs
- Kaiser: sewn, pleated masks with instructions in English, Spanish, Chinese
- Maker Mask: masks made of reusable grocery bag material (polypropylene), basic sewing skills needed
- Olson Mask: fitted mask with filter pocket, for people with more advanced sewing skills
Materials: Cotton and non-woven polypropylene are shown in studies to be the most effective and breathable mask materials for blocking droplets.
Cotton and similar fabrics in 2-layers block more than 90% of droplets from being emitted. Even a single-layer of t-shirt fabric can block more than 70% of droplets.
Non-woven polypropylene from matte reusable grocery bags can also be used, particularly as an outer layer with repellent properties.
Filters: Non-woven polypropylene can also be used as a reusable/washable filter. Other single-use filter materials that are commonly used are disposable coffee filters and paper towels. Be careful using vacuum bag material and avoid any containing fiberglass, which is dangerous when inhaled.
Maximizing mask protection
With evidence of more infectious variants circulating in the East Bay, we may be wondering if we should increase our prevention efforts.
Wearing two masks on top of each other (double-masking) and 3+ layered masks can provide more protection so long as you can keep them tight on your face. A new mask study by the CDC demonstrates that tight-fitting multilayered masks and double-masking can decrease exposure to aerosols by up to 95%.
Before you go out, please make sure your mask set up is comfortable and breathable enough to keep on your face! No matter how many layers a mask has, it will not be useful if you can’t keep it covering your nose and mouth.
Here are the qualities that make masks more protective, which we recommend using in indoor public settings (see higher/highest risk settings in our infographic below):
- Use tightly-woven fabric or non-woven material, like in surgical masks.
- Use multiple layers:
- 2 layers provide decent protection and 3 or more layers provide maximal protection.
- A non-woven layer, such as a disposable surgical-type mask or filter layer can help repel droplets.
- You can double-mask by using a fitted cloth mask with a disposable surgical-type mask, like in the diagram.
- Consider adding a face shield and/or goggles in the highest risk settings.
- Make it fit tight:
- Use tight/snug cloth masks.
- Reduce top gaps by using masks with adjustable nose wires.
- Reduce gaps in ear loop masks by tying knots near the sides. (video here)
- Make sure the mask has a tight seal all around, over your nose, sides of your mouth and under your chin.
- In high risk work settings, get fit-tested for an N95 mask (the gold standard in protective masks).
- Keep in mind that KN95 masks are not fit-tested and are less protective than N95 masks. Treat them like surgical masks.
References: Diagrams from Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021 by the CDC COVID-19 Emergency Response Team and …Importance of Face Masks for COVID-19 by Monica Gandhi and Linsey C. Marr. Scientific references for these masking tips are located here.
Do we have to wear face coverings if we intend to stay or work 6 feet apart?
- Yes, we need to wear face coverings in combination with at least 6 feet of distance. Neither of these interventions alone is perfect, so we need to use them in combination.
Do we have to wear face coverings when working or exercising outdoors?
- Yes, when outdoors we need to wear face coverings and maintain distance. While air circulation is better outdoors, and we may not intend to get close or talk with others, be prepared when it happens by wearing a face covering.
Can we wear our face mask or covering below or nose or mouth, especially in between contacts?
- No. Face coverings need to cover your nose and chin. The masks or coverings should fit well over the bridge of your nose, around the side of your cheeks, and below your chin. Respiratory droplets are exhaled and inhaled through both the nose and mouth. You may expose yourself to inhaling droplets that have gotten on the outside of your covering this way.
Do masks for COVID-19 protect against wildfire smoke and pollution?
- It depends. Smoke and air pollution particles are smaller than the droplets that carry the virus causing COVID-19. Cloth and hospital-type ear-loop masks generally do not filter out these tiny particles. To block smoke and pollution, use a non-medical N95 mask. Medical and non-medical N95 masks are tested to block at least 95% of these smaller particles when they fit well.
You can find all the references in this COVID-19 Harm Reduction document, which is updated regularly with new studies.