The use of face masks has become a widely recognized public health measure to limit the spread of respiratory illnesses, including COVID-19. These barriers function in two primary ways: they provide source control by blocking virus-containing aerosols and droplets released by the wearer, and they offer personal protection by filtering the air inhaled by the wearer. The effectiveness of any mask relies on a combination of its filtration material and how completely it seals to the face. Understanding these factors is necessary for selecting and using a mask to achieve the highest possible level of defense.
The Hierarchy of Mask Protection
The highest tier of protection comes from filtering facepiece respirators (FFRs), such as the N95, KN95, and FFP2 models. These respirators are certified to filter a minimum of 95% (N95/KN95) or 94% (FFP2) of airborne particles, including the most penetrating particle size of 0.3 microns. This high efficiency is achieved through multiple layers of non-woven polypropylene that utilize both mechanical trapping and an electrostatic charge to attract and hold tiny aerosols.
Surgical or medical masks occupy the middle tier, and their performance is rated by ASTM International standards, often classified as Level 1, 2, or 3. These masks are primarily designed to block large droplets and splashes, and their filtration efficiency for smaller aerosols typically ranges from 42% to 88% under a perfect seal condition. Unlike respirators, surgical masks are loose-fitting and are not designed to create a tight seal, which allows air to leak around the edges.
Cloth or fabric masks offer the lowest level of consistent protection, as their material weave is less effective at filtering fine aerosols. Studies have shown cloth masks filter a significantly lower percentage of viral-sized particles, with some designs blocking only 16% to 23% of 0.3-micron particles. The choice of mask should therefore align with the level of risk in a given environment.
Achieving a Secure Seal
A mask’s filtration rating is only relevant if the air you breathe passes through the filter material and not around the edges, as the seal prevents unfiltered air from leaking through gaps near the nose, cheeks, or chin. This seal is especially important for respirators like the N95, which are designed to achieve a tight fit around the entire perimeter of the face.
For N95 and similar masks, proper donning involves placing one strap at the crown of the head and the other at the nape of the neck, ensuring the straps do not cross. The metal nosepiece must then be firmly molded over the bridge of the nose using two fingers from both hands, avoiding a sharp pinch that can create peaks and compromise the seal.
To verify the fit, a user should perform a seal check. This involves covering the mask with both hands and either inhaling sharply to feel the mask pull inward (negative pressure check) or exhaling forcefully to ensure no air escapes around the edges (positive pressure check).
Common fit issues, such as glasses fogging, indicate air is escaping upward near the nose, which requires further adjustment of the nose wire or a better mask model. For surgical masks, which often fit loosely, using a mask fitter or placing a cloth mask over the surgical mask can help push the edges against the face to reduce gaps. A good fit is compromised by facial hair, particularly stubble or beards, which prevents the mask material from contacting the skin and makes a tight seal impossible.
Current Context for Mask Usage
The decision to wear a mask often depends on the current level of community transmission and the specific setting. Individuals are encouraged to use metrics like local COVID-19 hospital admission levels, often provided by public health authorities, to gauge the risk in their area.
Masking is now frequently recommended in high-risk settings, regardless of local case counts, due to the increased probability of encountering the virus. These locations include crowded indoor spaces, public transportation, and healthcare facilities. People who are at higher risk for severe illness, such as those who are immunocompromised or have underlying health conditions, may choose to wear a high-quality mask consistently in indoor public settings.
Furthermore, personal circumstances dictate masking choices, such as having a household member who is vulnerable or having a recent exposure to the virus. If an individual experiences COVID-19 symptoms or tests positive, wearing a mask for a period is generally advised when around others to prevent further spread.
Proper Handling and Reusability
To maintain the integrity and effectiveness of a mask, especially for reusable respirators, proper handling and storage are necessary. Before touching the mask, hands should be washed or sanitized. When removing a mask, always handle it by the straps or ear loops, avoiding contact with the front surface, which is considered contaminated.
For disposable respirators like N95s and KN95s, a rotation system is recommended to allow the electrostatic charge to regenerate and any trapped viral particles to become non-viable. The mask should be stored in a clean, dry, breathable container, such as a paper bag, between uses. Plastic bags should be avoided as they trap moisture, which can promote microbial growth and degrade the mask’s material.
A mask must be discarded immediately if it becomes visibly soiled, wet, or damaged. Signs of damage include stretched or broken straps, a loss of shape, or an inability to form a seal during the user check. If breathing becomes difficult, the filter media may be clogged, signaling it is time to replace the mask.