When and how to use masks - WHO Guidance

1) WHO recommends that persons with any symptoms suggestive of COVID-19 should:
• wear a medical mask, self-isolate, and seek medical advice as soon as they start to feel unwell with potential symptoms of COVID-19, even if symptoms are mild. Symptoms can include: fever, cough, fatigue, loss of appetite, shortness of breath and muscle pain. Other non-specific symptoms such as sore throat, nasal congestion, headache, diarrhoea, nausea and vomiting, have also been reported. Loss of smell and taste preceding the onset of respiratory symptoms have also been reported.(64, 65) Older people and immunosuppressed patients may present with atypical symptoms such as fatigue, reduced alertness, reduced mobility, diarrhoea, loss of appetite, delirium, and absence of fever.(26, 66, 67) It is important to note that early symptoms for some people infected with COVID-19 may be very mild and unspecific;
• follow instructions on how to put on, take off, and dispose of medical masks and perform hand hygiene;(68)
• follow all additional measures, in particular respiratory hygiene, frequent hand hygiene and maintaining physical distance of at least 1 metre (3.3 feet) from other persons.(42) In the context of the COVID-19 pandemic, it is recommended that all persons, regardless of whether they are using masks or not, should:
• avoid groups of people and crowded spaces (follow local advice);
• maintain physical distance of at least 1 metre (3.3 feet) from other persons, especially from those with respiratory symptoms (e.g. coughing, sneezing);
• perform hand hygiene frequently, using an alcohol-based handrub if hands are not visibly dirty or soap and water;
• use respiratory hygiene i.e. cover their nose and mouth with a bent elbow or paper tissue when coughing or sneezing, dispose of the tissue immediately after use, and perform hand hygiene;
• refrain from touching their mouth, nose, and eyes.
2) Advice to decision makers on the use of masks for the general public Many countries have recommended the use of fabric masks/face coverings for the general public. At the present time, the widespread use of masks by healthy people in the community setting is not yet supported by high quality or direct scientific evidence and there are potential benefits and harms to consider (see below). However, taking into account the available studies evaluating pre- and asymptomatic transmission, a growing compendium of observational evidence on the use of masks by the general public in several countries, individual values and preferences, as well as the difficulty of physical distancing in many contexts, WHO has updated its guidance to advise that to prevent COVID-19 transmission effectively in areas of community transmission, governments should encourage the general public to wear masks in specific situations and settings as part of a comprehensive approach to suppress SARS-CoV-2 transmission (Table 2).
WHO advises decision makers to apply a risk-based approach focusing on the following criteria when considering or encouraging the use of masks for the general public:
1. Purpose of mask use:
If the intention is preventing the infected wearer transmitting the virus to others (that is, source control) and/or to offer protection to the healthy wearer against infection (that is, prevention).
2. Risk of exposure to the COVID-19 virus due to epidemiology and intensity of transmission in the population:
if there is community transmission and there is limited or no capacity to implement other containment measures such as contact tracing, ability to carry out testing and isolate and care for suspected and confirmed cases.
depending on occupation:
Individuals working in close contact with the public (e.g., social workers, personal support workers, cashiers).
3. Vulnerability of the mask wearer/population:
for example, medical masks could be used by older people, immunocompromised patients and people with comorbidities, such as cardiovascular disease or diabetes mellitus, chronic lung disease, cancer and cerebrovascular disease.(69)
4. Setting in which the population lives:
settings with high population density (e.g. refugee camps, camp-like settings, those living in cramped conditions) and settings where individuals are unable to keep a physical distance of at least 1 metre (3.3 feet) (e.g. public transportation).
5. Feasibility:
availability and costs of masks, access to clean water to wash non-medical masks, and ability of mask wearers to tolerate adverse effects of wearing a mask.
6. Type of mask:
medical mask versus non-medical mask Based on these criteria, Table 2 provides practical examples of situations where the general public should be encouraged to wear a mask and it indicates specific target populations and the type of mask to be used according to its purpose. The decision of governments and local jurisdictions whether to recommend or make mandatory the use of masks should be based on the above criteria, and on the local context, culture, availability of masks, resources required, and preferences of the population.
Potential benefits/advantages
The likely advantages of the use of masks by healthy people in the general public include:
• reduced potential exposure risk from infected persons before they develop symptoms;
• reduced potential stigmatization of individuals wearing masks to prevent infecting others (source control) or of people caring for COVID-19 patients in non-clinical settings;(70)
• making people feel they can play a role in contributing to stopping spread of the virus;
reminding people to be compliant with other measures (e.g., hand hygiene, not touching nose and mouth). However, this can also have the reverse effect (see below);
• potential social and economic benefits. Amidst the global shortage of surgical masks and PPE, encouraging the public to create their own fabric masks may promote individual enterprise and community integration. Moreover, the production of non-medical masks may offer a source of income for those able to manufacture masks within their communities. Fabric masks can also be a form of cultural expression, encouraging public acceptance of protection measures in general. The safe re-use of fabric masks will also reduce costs and waste and contribute to sustainability.
Potential harms/disadvantages
The likely disadvantages of the use of mask by healthy people in the general public include:
• potential increased risk of self-contamination due to the manipulation of a face mask and subsequently touching eyes with contaminated hands;(48, 49)
• potential self-contamination that can occur if non-medical masks are not changed when wet or soiled. This can create favourable conditions for microorganism to amplify;
• potential headache and/or breathing difficulties, depending on type of mask used;
• potential development of facial skin lesions, irritant dermatitis or worsening acne, when used frequently for long hours;(50)
• difficulty with communicating clearly;
• potential discomfort;(41, 51)
• a false sense of security, leading to potentially lower adherence to other critical preventive measures such as physical distancing and hand hygiene;
• poor compliance with mask wearing, in particular by young children;
• waste management issues; improper mask disposal leading to increased litter in public places, risk of contamination to street cleaners and environment hazard;
• difficulty communicating for deaf persons who rely on lip reading;
• disadvantages for or difficulty wearing them, especially for children, developmentally challenged persons, those with mental illness, elderly persons with cognitive impairment, those with asthma or chronic respiratory or breathing problems, those who have had facial trauma or recent oral maxillofacial surgery, and those living in hot and humid environments.

If masks are recommended for the general public, the decision-maker should:
• clearly communicate the purpose of wearing a mask, where, when, how and what type of mask should be worn. Explain what wearing a mask may achieve and what it will not achieve, and communicate clearly that this is one part of a package of measures along with hand hygiene, physical distancing and other measures that are all necessary and all reinforce each other;
• inform/train people on when and how to use masks safely (see mask management and maintenance sections), i.e. put on, wear, remove, clean and dispose;

• consider the feasibility of use, supply/access issues, social and psychological acceptance (of both wearing and not wearing different types of masks in different contexts);
• continue gathering scientific data and evidence on the effectiveness of mask use (including different types and makes as well as other face covers such as scarves) in non-health care settings;
• evaluate the impact (positive, neutral or negative) of using masks in the general population (including behavioral and social sciences).
WHO encourages countries and community adopting policies on masks use in the general public to conduct good quality research to assess the effectiveness of this intervention to prevent and control transmission.
3) Types of mask to consider
Medical mask
Medical masks should be certified according to international or national standards to ensure they offer predictable product performance when used by health workers, according to the risk and type of procedure performed in a health care setting. Designed for single use, a medical mask’s initial filtration (at least 95% droplet filtration), breathability and, if required, fluid resistance are attributed to the type (e.g. spunbond or meltblown) and layers of manufactured non-woven materials (e.g. polypropylene, polyethylene or cellulose). Medical masks are rectangular in shape and comprise three or four layers. Each layer consists of fine to very fine fibres. These masks are tested for their ability to block droplets (3 micrometres in size; EN 14683 and ASTM F2100 standards) and particles (0.1 micrometre in size; ASTM F2100 standard only). The masks must block droplets and particles while at the same time they must also be breathable by allowing air to pass. Medical masks are regulated medical devices and categorized as PPE.
The use of medical masks in the community may divert this critical resource from the health workers and others who need them the most. In settings where medical masks are in short supply, medical masks should be reserved for health workers and at-risk individuals when indicated.
Non-medical mask
Non-medical (also referred to as “fabric” in this document) masks are made from a variety of woven and non-woven fabrics, such as polypropylene. Non-medical masks may be made of different combinations of fabrics, layering sequences and available in diverse shapes. Few of these combinations have been systematically evaluated and there is no single design, choice of material, layering or shape among the non-medical masks that are available. The unlimited combination of fabrics and materials results in variable filtration and breathability. A non-medical mask is neither a medical device nor personal protective equipment. However, a non-medical mask standard has been developed by the French Standardization Association (AFNOR Group) to define minimum performance in terms of filtration (minimum 70% solid particle filtration or droplet filtration) and breathability (maximum pressure difference of 0.6 mbar/cm2 or maximuminhalation resistance of 2.4 mbar and maximum exhalation resistance of 3 mbar).(71) The lower filtration and breathability standardized requirements, and overall expected performance, indicate that the use of non-medical masks, made of woven fabrics such as cloth, and/or non-woven fabrics, should only be considered for source control (used by infected persons) in community settings and not for prevention. They can be used ad-hoc for specific activities (e.g., while on public transport when physical distancing cannot be maintained), and their use should always be accompanied by frequent hand hygiene and physical distancing. Decision makers advising on type of non-medical mask should take into consideration the following features of non-medical masks: filtration efficiency (FE), or filtration, breathability, number and combination of material used, shape, coating and maintenance.
a) Type of materials: filtration efficiency (FE), breathability of single layers of materials, filter quality factor
The selection of material is an important first step as the filtration (barrier) and breathability varies depending on the fabric. Filtration efficiency is dependent on the tightness of the weave, fibre or thread diameter, and, in the case of non-woven materials, the manufacturing process (spunbond, meltblown, electrostatic charging).(49, 72) The filtration of cloth fabrics and masks has been shown to vary between 0.7% and 60%.(73, 74) The higher the filtration efficiency the more of a barrier provided by the fabric.
Breathability is the ability to breathe through the material of the mask. Breathability is the difference in pressure across the mask and is reported in millibars (mbar) or Pascals (Pa) or, for an area of mask, over a square centimeter (mbar/cm2 or Pa/cm2). Acceptable breathability of a medical mask should be below 49 Pa/cm2. For non-medical masks, an acceptable pressure difference, over the whole mask, should be below 100 Pa.(73)
Depending on fabric used, filtration efficiency and breathability can complement or work against one another. Recent data indicate that two non-woven spunbond layers, the same material used for the external layers of disposable medical masks, offer adequate filtration and breathability. Commercial cotton fabric masks are in general very breathable but offer lower filtration.(75) The filter quality factor known as “Q” is a commonly used filtration quality factor; it is a function of filtration efficiency (filtration) and breathability, with higher values indicating better overall efficiency.(76) Table 3 shows FE, breathability and the filter quality factor, Q, of several fabrics and non-medial masks.(73, 77) According to expert consensus three (3) is the minimum Q factor recommended. This ranking serves as an initial guide only.
It is preferable not to select elastic material for making masks; during wear, the mask material may be stretched over the face, resulting in increased pore size and lower filtration efficiency throughout use. Also, elastic materials may degrade over time and are sensitive to washing at high temperatures.
b) Number of layers
A minimum of three layers is required for non-medical masks, depending on the fabric used. The innermost layer of the mask is in contact with the wearer’s face. The outermost layer is exposed to the environment.(78)
Fabric cloths (e.g., nylon blends and 100% polyester) when folded into two layers, provides 2-5 times increased filtration efficiency compared to a single layer of the same cloth, and filtration efficiency increases 2-7 times if it is folded into 4 layers.(75) Masks made of cotton handkerchiefs alone should consist of at least 4 layers, but have achieved only 13% filtration efficiency.(73) Very porous materials, such as gauze, even with multiple layers will not provide sufficient filtration; only 3% filtration efficiency. (73)
It is important to note that with more tightly woven materials, as the number of layers increases, the breathability may be reduced. A quick check for breathability may be performed by attempting to breathe, through the mouth, and through the multiple layers.
c) Combination of material used
The ideal combination of material for non-medical masks should include three layers as follows: 1) an innermost layer of a hydrophilic material (e.g. cotton or cotton blends); 2), an outermost layer made of hydrophobic material (e.g., polypropylene, polyester, or their blends) which may limit external contamination from penetration through to the wearer’s nose and mouth; 3) a middle hydrophobic layer of synthetic non-woven material such as polyproplylene or a cotton layer which may enhance filtration or retain droplets.
d) Mask shape
Mask shapes include flat-fold or duckbill and are designed to fit closely over the nose, cheeks and chin of the wearer. When the edges of the mask are not close to the face and shift, for example, when speaking, internal/external air penetrates through the edges of the mask rather than being filtered through the fabric. Leaks where unfiltered air moves in and out of the mask may be attributed to the size and shape of the mask.(79)
It is important to ensure that the mask can be held in place comfortably with little adjustment using elastic bands or ties.
e) Coating of fabric
Coating the fabric with compounds like wax may increase the barrier and render the mask fluid resistant; however, such coatings may inadvertently completely block the pores and make the mask difficult to breathe through. In addition to decreased breathability unfiltered air may more likely escape the sides of the mask upon exhalation. Coating is therefore not recommended.
f) Mask maintenance
Masks should only be used by one person and should not be shared. All masks should be changed if wet or visibly soiled; a wet mask should not be worn for an extended period of time. Remove the mask without touching the front of the mask, do not touch the eyes or mouth after mask removal. Either discard the mask or place it in a sealable bag where it is kept until it can be washed and cleaned. Perform hand hygiene immediately afterwards. Non-medical masks should be washed frequently and handled carefully, so as not to contaminate other items.
If the layers of fabrics look noticeably worn out, discard the mask. Clothing fabrics used to make masks should be checked for the highest permitted washing temperature. If instructions for washing are indicated on the clothing label, verify if washing in warm or hot water is tolerated. Select washable fabrics that can be washed. Wash in warm hot water, 60°C, with soap or laundry detergent. Non-woven polypropylene (PP) spunbond may be washed at high temperatures, up to 125°C.(72) Natural fibres may resist high temperature washes and ironing. Wash the mask delicately (without too much friction, stretching or wringing) if nonwoven materials (e.g. spunbond) are used. The combination of non-woven PP spunbond and cotton can tolerate high temperatures; masks made of these combinations may be steamed or boiled.
Where hot water is not available, wash mask with soap/detergent at room temperature water, followed by either i) boiling mask for one minute OR ii) soak mask in 0.1% chlorine for one minute then thoroughly rinse mask with room temperature water, to avoid any toxic residual of chlorine. WHO is collaborating with research and development partners and the scientific community engaged in textile engineering and fabric design to facilitate a better understanding of the effectiveness and efficiency of non-medical masks. WHO urges countries that have issued recommendations on the use of both medical and non-medical masks by healthy people in community settings to conduct research on this important topic. Such research needs to look at whether SARS-CoV-2 particles can be expelled through non-medical masks of poor quality worn by a person with symptoms of COVID-19 while that person is coughing, sneezing or speaking. Research is also needed on non-medical mask use by children and other medically challenging persons and settings as mentioned above.
3. Alternatives to non-medical masks for the general public
In the context of non-medical mask shortage, face shields may be considered as an alternative noting that they are inferior to mask with respect to prevention of droplet transmission. If face shields are to be used, ensure proper design to cover the sides of the face and below the chin. In addition, they may be easier to wear for individuals with limited compliance with medical masks (such as those with mental health disorders, developmental disabilities, deaf and hard of hearing community and children).
Guidance on the use of medical masks for the care of COVID-19 patients at home WHO provides guidance on how to care for patients with confirmed and suspected COVID-19 at home when care in a health facility or other residential setting is not possible.(4) Home care may be considered when inpatient care or isolation in non-traditional settings is unavailable or unsafe (e.g. capacity is limited and resources are unable to meet the demand for care services). If feasible, a trained health worker should conduct an assessment to verify whether the patient and the family are able to comply with recommended measures for home-care isolation (e.g. hand hygiene, respiratory hygiene, environmental cleaning, limitations on movement around or from the house) and to address safety concerns (e.g. accidental ingestion of and fire hazards associated with using alcohol-based handrubs). Specific IPC guidance for home care should be followed. (4)
Persons with suspected COVID-19 or mild COVID-19 symptoms and no risk factors should:
• be isolated in a medical facility if confirmed, or self-isolate at home if isolation in a medical or other designated facility is not indicated or not possible;
• perform hand and respiratory hygiene frequently;
• keep a distance of at least 1 metre (3.3 feet) from other people;
• wear a medical mask as much as possible; the mask should be changed at least once daily. Persons who cannot tolerate a medical mask should rigorously apply respiratory hygiene (i.e. cover mouth and nose with a disposable paper tissue when coughing or sneezing and dispose of it immediately after use or use a bent elbow procedure and then perform hand hygiene);
• limit movement and minimize shared space;
• avoid contaminating surfaces with saliva, sputum or respiratory secretions;
• improve airflow and ventilation in their living space by opening windows and doors as much as possible;
• ensure adequate cleaning and disinfection of touch surfaces, near where the patient is being cared for, such as bedside tables, bedframes, and other bedroom furniture; electronic touchscreens, keyboards, and controls; and bathroom fixtures.
Caregivers or those sharing living space with people with suspected COVID-19 or with mild COVID-19 symptoms should:
• perform hand hygiene according to the 5 Moments of Hand Hygiene,(80) using an alcohol-based handrub if hands are not visibly dirty or soap and water when hands are visibly dirty;
• keep a distance of at least 1 m from the affected person when possible;
• wear a medical mask when in the same room as the affected person;
• dispose of any material contaminated with respiratory secretions (disposable tissues) immediately after use and then perform hand hygiene;
• improve airflow and ventilation in the living space by opening windows as much as possible;
• ensure adequate cleaning and disinfection of touch surfaces in the patient’s room, such as bedside tables, bedframes and other bedroom furniture; electronic touchscreens, keyboards, and controls; and bathroom fixtures.
Guidance on mask management
For any type of mask, appropriate use and disposal are essential to ensure that they are as effective as possible and to avoid any increase in transmission. WHO offers the following guidance on the correct use of masks, derived from best practices in health care settings:
• perform hand hygiene before putting on the mask;
• place the mask carefully, ensuring it covers the mouth and nose, adjust to the nose bridge, and tie it securely to minimize any gaps between the face and the mask;
• avoid touching the mask while wearing it;
• remove the mask using the appropriate technique: do not touch the front of the mask but untie it from behind.
• after removal or whenever a used mask is inadvertently touched, clean hands with an alcohol-based handrub, or soap and water if hands are visibly dirty;
• replace masks as soon as they become damp with a new clean, dry mask;
• do not re-use single-use masks;
• discard single-use masks after each use and dispose of them immediately upon removal.

WHO continues to monitor the situation closely for any changes that may affect this interim guidance. Should any factors change, WHO will issue a further update. Otherwise, this interim guidance document will expire 2 years after the date of publication.

Courtesy :  from WHO covid19 advice for public