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 pandemic, the US made the fatal 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.
Masks are effective at preventing respiratory droplets coming out of the wearer’s nose and mouth getting into shared air (“source control”) as well as provide protection for the wearer, reducing our exposure to droplets and aerosols that may contain the virus that causes COVID-19.
Aim to wear masks that are multilayered, fit well without gaps, and are comfortable.
- The best protection (against COVID and wildfire smoke) is with genuine KF94, KN95 and N95 masks that fit well.
- Next best is double masking with a tight-fitting cloth mask over a surgical-type mask, or tight-fitting cloth masks with tested, high-quality filters that span the entire mask edge-to-edge.
- Good protection can be achieved with a surgical-type mask with gaps minimized, such as with the “knot and tuck” method. (picture here; video here)
- A cloth mask alone is better than no mask!
See more details on masking below.
- 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 high quality and 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.
Multiple layers including a non-woven layer is better: it’s best to have at least 2 and ideally 3 or more layers, including tightly-woven fabric for a physical barrier and tight fit plus non-woven polypropylene layers for an electrostatic droplet-repelling layer. This includes disposable “surgical” ear-loop masks, KF94s, KN95s and N95s.
Style/fit: The better the covering fits around the nose, chin and cheeks without gaps, the better it blocks. Sewn cloth masks with ear loops or ties that go around the head block better than bandanas, gaiters and scarves that are looser. Gaps in surgical masks can be reduced by tying knots in the ear loops, also known as the “knot and tuck” method (video here).
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 potential virus-infected droplets to dry and die. Don’t wipe it down or make it wet because it disrupts its droplet repellent properties.
Maximizing mask protection
With evidence of more infectious variants like delta circulating, we may be wondering if we should increase our prevention efforts. The answer is: Yes!
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 mask study by the CDC demonstrates that if everyone in a room wears tight-fitting multilayered masks or double-masks, we 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 and non-woven polypropylene material. Tightly-woven fabric provides a physical barrier for droplets. Non-woven polypropylene uses electrostatic properties to repel droplets/aerosols and is used in surgical masks, KF94s, N95s, KN95s and some mask filters.
- Use multiple layers:
- 2 layers provide moderate protection and 3 or more layers provide maximal protection.
- A tightly-woven fabric creates a physical barrier and tight fit.
- A non-woven polypropylene layer, such as in a disposable surgical-type mask or filter to repel droplets and aerosols.
- 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 the “knot and tuck” method to reduce side gaps in surgical masks
- Use tight/snug cloth masks.
- Reduce top gaps by using masks with adjustable metal nose wires.
- Reduce side gaps in ear loop (surgical) masks by tying knots near the sides, known as the “knot and tuck” method. (picture here; video here)
- Make sure the mask has a tight seal all around, over your nose, sides of your mouth and under your chin.
- Small and extra-small KF94s are available as a high-quality, well-fitted mask option for children and smaller faces.
- 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.
For a deeper dive into masks, check out:
- Check out this video of masking science FAQs and info about KF94s from Aaron Collins, aerosol engineer and mask nerd.
- Spreadsheet of all masks tested by Aaron Collins.
- Mask recommendations for kids from aerosol scientists Linsey Marr, PhD and Aaron Prussin, PhD at Virginia Tech.
- Video on masking for kids under 12 and companion spreadsheet of tested kids masks from Aaron Collins (also a parent).
- CDC’s list of trusted N95s and guide for spotting fake N95s.
- Home fit-testing process from Dr. Richard Corsi, aerosol scientist and Dean of Engineering at UC Davis.
- Basically, cool a little mirror or pair of glasses in the fridge, then put it above, to the sides and below the mask while it’s on your face and look for condensation/steam from your breath to check for gaps.
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, indoors. COVID-19 is spread by droplets and aerosols which can linger in the air in poorly ventilated indoor settings. The 6 foot rule is somewhat arbitrary since aerosols can travel long distances indoors. For better protection, especially if you’re not vaccinated or around vulnerable people, wear face coverings in combination with at least 6 feet of distance. Try to open windows and doors and/or turn on HVAC systems or air purifiers for ventilation too. None of these interventions alone is perfect, so we need to use them in combination. When outdoors in uncrowded settings and where you can maintain 6+ feet of distance from others, masking is less necessary for protection since aerosols quickly disperse into the open air.
Do we have to wear face coverings when working or exercising outdoors?
- If you’re not vaccinated or immunocompromised it’s best to wear face coverings and maintain distance, especially in crowded outdoor settings. Vaccinated people who live or work with vulnerable people can also reduce the risk of transmission by wearing masks in crowded outdoor settings. While air circulation is better outdoors, and we may not intend to get close or talk with others, be prepared when it happens by having a mask handy or by keeping a mask on.
Can we wear our face mask or covering below or nose or mouth, especially in between contacts?
- It’s best not to. 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?
- Some masks do. 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 tested, certified and tightly-fitting N95, KN95 or KF94 mask. These masks are tested to block at least 94-95% 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.
Instructions to make your own masks:
With highly infectious variants circulating and a much better mask supply, we no longer recommend that you make your own masks. However, if you aren’t able to purchase masks and/or want to make your own reusable masks for use in lower risk settings or for double-masking with surgical masks, here are the DIY mask instructions we’ve used:
- 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: Tightly-woven 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. When cleaning these, we recommend to run them through the dryer or rubbing them with rubber gloves after they dry to regain electrostatic, droplet-repelling 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.