“Masks are incredible. … they have saved lot of lives … A mask is cheap, and easy to stockpile. Masks are magical and they don’t have much downside.”

  • Bill Gates, founder BMGF which has committed over US$2 billion to the global COVID-19 response.

Covid’s resurgence has once again raised the question how much protection a mask gives if you are wearing one, but others around you are mask free?

Masks give most protection when everyone is wearing it. Because a sizeable percentage of the viral particles exhaled by an infected person are trapped and do not escape into the air. Thus, fewer viral particles are in the air and the mask is likely to block these.

But wearing a mask gives you some protection even when others are not wearing it. How much protection it gives depends on the type of mask, on how well it fits, on the virus density (number of viral particles) in your environment, on how much time you are exposed to the virus, and on the type of virus.

Types of masks and respirators and the protection they give

In several tests, types of masks and respirators and the percentage-protection they gave from lowest to highest were:

  • A simple cotton mask, 17 percent to 27 percent.
  • A surgical mask, 47 percent to 50 percent.
  • A surgical mask covered with a cloth mask (double masking), 83 percent.
  • A two-layer cloth mask made of flexible, tightly woven fabric, combined with a filter material (like a coffee filter or surgical mask), 70 percent to 90 percent.
  • A loose-fitting non-surgical N 95 respirator, 57 percent to 86 percent.
  • A tightly sealed non-surgical N 95 respirator, 79 percent to 90 percent.
  • KN95 and KF 94 respirators are not NIOSH-approved like the N 95 but may give similar protection.
  • Surgical N 95, N99, and N100 respirator give 95% to 99.5% but should be reserved for health care professionals.

In a few other studies cloth masks gave 60%, surgical masks 76% and N95 respirators 99% protection.

Cloth and surgical mask filter out sprays and large droplets and particles that my contain virus. N95 and higher masks filter out large as well as small particles and thus give better protection.


A face shield gives only limited protection. It may be used along with a mask for added protection. Or may have to be used if wearing a mask is not feasible. The shield should wrap around your face and extend below the chin.

World health Organisation (WHO) has classified Alpha, Gama Beta, Delta, and Omicron variants of covid as a variant of concern. These variants “are more infectious, more likely to cause breakthrough infections or reinfections in those who are vaccinated or previously infected, cause severe disease, evade diagnostic tests, or resist antiviral treatment.” These also cause more hospitalization and more deaths.

N95, KN95, KF94, N99 and N100 respirators provide the best protection against these variants and especially against Omicron subvariant BA.2 (stealth omicron), which is far more contagious, and is now the dominant strain.

Masks with valves make breathing easier but do not filter the air breathed out. Therefore, these should not be used and have been banned at many places.

Surgical masks are disposable. N95 and higher masks are also disposable, but scientists are investigating ways to disinfect and reuse them.

Mask does not increase carbon di oxide level in the air you breathe

How to wear the mask

Mask should fit the contours of your face and be snug over your nose, mouth, and chin and seal these with no gaps. When you breathe out, air should come out of the front of the mask, not through the edges of the mask. Chose mask with bendable nose strip so that the air does not leak out from the top of the mask. Prefer masks with head straps or ties. These fit better than ones with ear loops.

Do not add layers to the mask if it makes breathing difficult. Do not use layers or another mask over N95 and higher masks. Wash or sanitize hands before and after putting on mask or removing it. Put on and remove mask lifting ear or head loops without touching the mask. Do not touch the mask while wearing it. If you accidentally touch the mask, wash, or sanitize hands immediately. Dispose off wet and dirty masks. Wash cloth masks by hand or in a washing machine. Discard disposable masks after wearing once.

Masks should not be used by children under the age of two, by people having breathing trouble, and when exercising.

The 15-minutes guideline

The Centers for Disease Control and Prevention (CDC) of the US guideline is that if you are within six feet of a covid infected person for 15 minutes or more, you are at risk of being infected.

But this is only a guideline, not a fixed rule. CDC has clarified that even a briefer exposure can cause infection. If you are in a crowded, poorly ventilated, enclosed space and the infected persons are coughing, laughing, or singing loud, you may get infected even if you were more than six feet away or were in the setting for less than 15 minutes. If you were in windy outdoors, 15 minutes exposure may not be that risky.

When traveling, infection risk is the lowest in air travel, higher in train and highest in bus travel. In a study, wearing the mask reduced the infection risk by 54% during air travel.

Elevated risk groups

Persons above age 60, and those of any age who have health conditions such as diabetes mellitus, cardiovascular disease, obesity, chronic respiratory disease, cancer, or are immunocompromised, are at higher risk of becoming seriously ill or dying from covid. They must take exceptional care to protect themselves against infection. 


The last four pandemics morphed into endemic within one and-half to two years of emerging. That does not seem to be happening for covid. We are uncertain if future variants of covid will emerge and when. For the pandemic to end, covid must be eliminated across the world; or 55-80% of population must be immune because of vaccination or infection. Neither is likely to happen. The other uncertainty is that we do not know if the vaccine will be a onetime affair or will need periodic booster doses.

Covid is with us for the near future. We must protect ourselves from it. Mask gives some protection from infection. But vaccination and booster shots are the best protection against infection. For better protection we should follow all the guidelines. Physical distance, frequent hand wash, avoid crowded, poorly ventilated, closed spaces, prefer interactions outdoors rather than indoors, be fully vaccinated with all the doses and booster shots. You are fully vaccinated two weeks after the second dose.

Covid is reshaping India. By taking care to reduce the transmission of covid, we can ensure that post-covid India is in a better shape than pre-covid India. The future is ours to shape.



1. How well do face masks protect against COVID-19?

2. Coronavirus disease (COVID-19): Masks

3. Should You Still Wear a Mask?

4. Tracking SARS-CoV-2 variants

5. Here’s what the new CDC guidance on 15 minutes of COVID-19 exposure means for you

Dr. Sadhanakala

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