- Wearing two masks or a cloth mask with three layers of material could up your protection from SARS-CoV-2 infection.
- Cloth masks with a valve don’t work, since it sends a jet of your breath out of the mask, increasing the chances of making others ill.
- When you breathe out, air should not escape from the edges of your mask, instead it should move through the fabric.
“Place the candle one metre in front of you. Take a big breath in, and blow it out. Excellent. Now put on your mask and try again.”
This was my pre-pandemic party trick for presenting infection control training to healthcare workers.
Usually, the doctors and nurses would eye the surgical mask with some suspicion, not convinced that it would do much to capture the breath of the person volunteering to do this demonstration.
But seeing your colleagues struggle to blow out a simple candle is a persuasive visual demonstration of how masks can help prevent the spread of disease, by capturing someone’s respiratory droplets.
Now that a new, more infectious SARS-CoV-2 (the virus that causes COVID-19) variant, known as 501Y.V2, is dominant in South Africa, we have good reason to look for better masks that offer more personal protection. Because new variants have also been detected in Europe, the German airline, Lufthansa, has, for instance, announced that passengers are now required to wear medical grade masks on board.
But what does the ideal mask look like and how should you choose one? We break it down for you.
How do masks work?
Masks prevent the spread of COVID-19 by trapping infectious respiratory droplets — that contain the SARS-CoV-2 virus — when you breathe, speak or cough before they become suspended in the air.
Because many people who are ill with COVID-19 are asymptomatic, and the disease is most contagious two days before symptoms appear, it makes sense to wear a mask whenever you have contact with someone who is not living in the same household as you.
The infectious droplets become stuck in the tightly woven fibres of a mask – both when you are breathing out (the mask then protects others against you) and when you’re breathing in (that’s when the mask protects you against the respiratory droplets of others).
Although it is easy to visualise your mask to work like a sieve (filtering out the larger particles and allowing the smaller ones to slip through) there is more to masks than what meets the eye.
Masks with multiple layers present an obstacle course for respiratory droplets. How well they are able to do this, is referred to as their filtration efficacy. Imagine the inside of a mask looks like a passageway — covered in thick, sticky spider webs coming from various angles.
The infectious respiratory droplets are trying to weave through. The big ones might get stuck immediately, not able to fit through the gaps in the web. But the smaller ones, with a bit of turbulent breath, might be blown into the traps which they then get stuck to.
Wouldn’t it be amazing if the spiderwebs could then also, through some magnetic force, attract the respiratory droplets? Well, this is exactly why a respirator (explained below) has an additional way of adding protection — it uses an electrostatic charge to capture more particles.
What type of masks are available and what’s the difference between them?
There are three types of masks.
A medical mask is sometimes also called a surgical mask, disposal face mask or medical procedure mask — those are the type of masks that you would normally buy at a pharmacy or vendors such as Dis-Chem. Although there are a variety of options on the market, they mostly contain three to four layers, one which will usually be made of polypropylene (a tough type of plastic that is also used for the packaging of consumer products). Some medical masks have an outside layer that is waterproof and that can, for example, protect a surgeon against splashes of blood. Disadvantages are that they often do not have a tight fit and they need to be disposed of after one use. Although medical masks are recommended for use by the public by the World Health Organisation (WHO) and the Centres for Disease Control (CDC), South Africa’s mask wearing guidelines from April 2020 still focus on cloth masks for use by the public or ‘another appropriate item’.
A respirator is usually a bit thicker than a medical mask, but is also made of multiple layers of polypropylene. In the United States, the National Institute for Occupational Safety and Health tests and approves these respirators, and according to specifications, they are called N95 respirators. The N stands for Not resistant to oil (for that you need a P95 respirator), and the 95 means the mask filters out at least 95% of airborne particles. There is also an European Union equivalent (FFP2 respirators) and respirators made in China (KN95 respirators).
Unfortunately, counterfeit respirators are rife. KN95 respirators have recently come under fire in South Africa and abroad after some of the batches failed quality standards. Respirators are currently not recommended for use in South Africa by the public, because supply chains are still under strain.
The third type of mask — a cloth mask — can be made of a variety of fabrics, and this influences how well they work. Cloth masks are often more stylish, and they’re also reusable. Their biggest disadvantage is that they vary in how effective they are. But if you choose a cloth mask with the right features, it can offer the same protection or even improved protection compared to a single surgical mask.
What about masks with valves?
Thinking about the mechanism by which masks work, helps to understand why you should avoid masks with valves or face shields as a mask substitute. Masks with valves bypass this obstacle course of the mask when you breathe out, directing a jet of your breath through the valve, with the risk of making others ill.
- READ MORE: How wearing a mask can slash COVID-19 deaths
Recommendations against masks with valves were made by the South African department of trade and industry in October 2020. A face shield is not a sufficient replacement, because the infectious droplets simply skirt around the edges along with the air flow.
Should you “double mask”?
‘Double masking’ — wearing a surgical mask beneath a tighter fitting cloth mask — has also been added to CDC guidance on mask wearing, based on research that found this combination to significantly increase protection against infection. The study found that double masking is a good option if your cloth mask is only made of one layer of material, because a single layer doesn’t offer enough filtration to be protective to the person wearing it. Surgical masks often do not have a good enough fit, and that is why the tighter, more stretchy cloth mask can help.
But double isn’t always better — two surgical masks, or any mask and a respirator should not be worn together. Another equally effective option is to wear one cloth mask with the optimal number (three) of layers and type of material.
How many layers does a mask need and does the type of material used, matter?
The WHO, CDC and South African department of trade, industry and competition have all made recommendations for cloth mask specifications. The advice they provide aligns well: the optimal cloth mask should have three layers of material and the type of material is also important.
- The inside layer should feel comfortable against your skin, and should ideally be made of an absorbent material, such as cotton or a cotton-blend. The absorbent material can help make the mask more comfortable to wear, instead of small droplets building up on the inside of it.
- The middle layer (which can be a removable) should ideally be made of material that is a good filter, such as polypropylene. Washable, spunbond polypropylene is commonly used in the clothing and furniture industry and not used to manufacture personal protective equipment for health workers. The single use version of polypropylene is one of the components of a medical grade surgical mask.
- The outer layer could be made of a non-absorbent material, with the WHO recommending fabrics such as polyester, or a polyester blend. The reason for choosing a non-absorbent material is to prevent the mask from becoming wet from the outside.
So how do you know if your cloth mask has three layers? The easiest way is to check with the manufacturer when buying the mask. The CDC also recommends checking whether your mask is able to block out the light when you hold it close to a light source. This is a way to get a rough estimate of how good your mask is at filtration.
How do you know if your mask fits?
A mask made of the right material, but that fits badly, is only half-way there. The CDC says that “a common problem with some masks is that there can sometimes be gaps between the mask and the mask wearer’s face”.
“When there are gaps, air with respiratory droplets containing the virus can leak in and out around the edges of the mask (on the top or the sides). To help prevent air leakage, masks should fit snugly against the sides of the face and not have gaps,” the CDC explains.Masks that use a nose clip to avoid air leaking and that tie behind your head instead of having ear loops can often help. A slightly less stylish option is a rubber brace (also called a mask fitter) worn over the mask, that can improve the fit and help prevent leaks. Other simple alterations also recommended by the CDC includes tying the ear loops at the edge of the mask and tucking any additional fabric underneath the knotted area so that the mask fits closer to your face.
Indoor gatherings are always a risk — even with a mask
If you are indoors, in a poorly ventilated room, even if you are 1.5 metres apart and wearing a mask, there is still a significant risk of COVID spreading. This is an important nuance: wearing a mask helps to reduce your risk, and it is worth finding a better mask, but it still doesn’t remove the risk entirely.
Nowadays, we don’t need candle party tricks to persuade each other that masks are effective. But looking for a better mask is warranted. A mask made of one layer is better than no mask, but three layers are what we should aim for in a cloth mask. A filter layer of polypropylene can be a valuable add in. If your mask is made of one layer, wear it over a surgical mask.
Helene-Mari van der Westhuizen is a South African medical doctor and doctoral researcher in the Nuffield department of primary care health sciences at Oxford University, studying TB infection control in rural settings in South Africa. Van der Westhuizen recently co-authored a review article on masks published in January in the Proceedings of the National Academy of Sciences of the United States of America.