Updated September 7, 2023
Confused about masks? You’re not alone. There have been many confusing messages about masks. Early in the pandemic, the US made the fatal mistake of not recommending masks. Now we know better: Scientific evidence overwhelmingly shows that masks protect ourselves and others from COVID-19.
Wear masks that are multilayered, fit well without gaps, and are comfortable, especially in indoor and crowded settings when the local COVID transmission level is high and if you want to prevent infection.
- The best protection is with a genuine N95 mask that fits well without gaps. (Here’s a list of N95s.)
- Next best is a genuine KN95 or KF94 mask that fits well without gaps. (Here’s a list of KN95s and KF94s.)
- Good protection can be achieved with double masking with a tight-fitting cloth mask over a surgical-type mask.
- OK protection can be achieved with a surgical-type mask with gaps minimized, such as with the “knot and tuck” method. (picture here; video here) or with a mask brace.
- A cloth mask is better than no mask!
Umoja Health Community Hub offers free N95s and other masks at their North Oakland site at 750 Aileen Street, Oakland 94609, Monday-Tuesday-Wednesday, 10 am to 2 pm, 1-888-763-0007. They offer N95s and other masks, hand sanitizer, rapid antigen tests and printed resources at this location.
From November 1, 2023 through April 30, 2024, there is a Bay Area mask requirement for workers in high risk health settings: Staff and other workers in specified health facilities (General Acute Care Hospitals, Long Term Acute Care Hospitals, Psychiatric Hospitals, Skilled Nursing Facilities, Dialysis Centers, and Infusion Centers) in Alameda County and Contra Costa County are required to wear high-quality, well-fitting masks in patient care areas. Sonoma and San Mateo counties will have the same requirement. San Francisco already has a year-round masking requirement for health care workers.
See more details on masking below.
Why are masks helpful?
1. People without symptoms spread COVID-19.
Studies show that nearly half of 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 when around other people, especially indoors.
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 polypropylene layer is better: it’s best to have 3 or more layers, including tightly-woven fabric for a physical barrier and tight fit plus non-woven polypropylene layers for electrostatic droplet-repelling layers. 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) or with a mask brace (like from Fix The Mask).
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, discard disposable ones, or follow the reuse guidelines below after one trip out in the community.
Reusing N95, KN95 and KF94 masks (aka “respirators”)
- 5 uses for 5 weeks: This is a strategy used in health care work settings.
- Have one N95 mask for each day of the week, kept separate in a brown paper bag labeled with the day of the week.
- Use each mask for 5 days; i.e. Monday mask will be used for 5 Mondays.
- Put the used mask bag in a well-ventilated area so it can dry completely between uses and viral particles inactivate.
- If you don’t have 5 masks or enough to wait a week in between use, give each mask ~3 days between uses to dry completely.
- A mask can be reused for a total of ~40 hours as long as it stays clean, dry, fits tight and maintains its shape. If you use the mask for short periods, such as going into the store for an hour or so, running indoor errands, etc. you can continue to wear it for more than 5 uses.
- Don’t wipe the mask down or make it wet because it disrupts its droplet repellent properties.
- When putting on a reused mask:
- Do not touch the inside surfaces of the N95 when putting it on.
- Inspect before putting on the mask to make sure it’s clean, dry and has maintained its shape.
- Make sure all the edges seal tight before going into a room with other people.
- It’s safer to keep the mask on between multiple people/settings in a single day rather than taking it off and on repeatedly.
Maximizing mask protection
With highly infectious variants circulating, we may be wondering if we should increase our prevention efforts. The answer is: Yes!
- The best protection is with a genuine N95 mask with a headband that fits well without gaps.
- Next best is genuine KN95 or KF94 mask with ear-loops that fits well without gaps. N95, KN95 and KF94 masks are also called “respirators.”
- Good protection can be achieved with double masking with a tight-fitting cloth mask over a surgical-type mask or a mask brace. See below.
A case control study of real-world mask wearing among randomly-selected California residents found that people who consistently wore N95 or KN95 respirator masks in indoor public settings were the least likely to test positive for COVID-19, followed by people wearing surgical masks, followed by people wearing cloth masks, as compared to people who did not wear masks.
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 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:
- 3 or more layers provide better 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 uses an electrostatic property 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).
- You can also reduce gaps using a mask brace, such as these from Fix the Mask.
- 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. The Korean FDA also has a portal to check for genuine KF94s, though it’s currently only in Korean.
- In the Bubble podcast on masking and ventilation with Aaron Collins and Richard Corsi.
- 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.
Should we still wear masks if we are 6 feet apart?
- Yes, especially indoors when cases are high. 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.
Should we wear masks when outdoors?
- When cases are high, it’s safer to wear a mask in outdoor crowded settings and when talking in close range. If you’re immunocompromised or not vaccinated, it’s best to wear a respirator (N95, KN95, KF94) 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, we can still transmit the virus when talking or breathing heavily in close range, so be prepared with a mask.
Can we wear our mask below or nose or mouth, especially in between contacts?
- It’s best not to. To be effective, masks need to cover your nose and chin. Masks 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 inhale droplets that have gotten on the outside of your masks if you repeatedly move your mask around your face.
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 surgical ear-loop masks 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 respirator masks are tested to block at least 94-95% of these smaller particles when they fit well.
You can find scientific mask study references in this COVID-19 Harm Reduction document.