Can a mask be "worse than nothing"?
Text updated on 2020-05-30
A mask that is not properly put on, poorly used, or of poor filtering quality gives the illusion of protection, thus exposing the wearer and others around him/her. To protect others and oneself, a mask must be filtering, breathable, and waterproof, and even then it does not replace physical distancing!
To put on a mask is to protect others and also to protect yourself. It's an essential barrier gesture when you don't know who's contagious or vulnerable. The mask serves as both a physical and symbolic barrier to embody the attention one pays to preventing the transmission of the virus.
If wearing the mask makes the wearer feel too comfortable, it can often decrease the physical distancing measures, which can then become problematic. Talking too close or touching each other, even with a mask on, carries a risk of contamination. Especially if the mask is incorrectly put on, misused, worn-out, or of poor quality.
(1) A mask is misused if it does not cover the mouth and nose at the same time.
(2) A mask is incorrectly fitted if the seal around the mask is not ensured: e.g., a mask without nose clip, a mask that does not cover chin or cheeks properly. A mask can be checked for leaks by putting on your mask, covering it with plastic or well-washed hands, and inhaling heavily. If it's tight, the mask sticks to your face and you can't breathe.
(3) A mask is bad if the cloth doesn't filter well: A cotton cloth must be very tight to make a good sieve otherwise even two layers won't protect. The polypropylene fibers in new surgical masks and FFP2 have a quasi-permanent electrical charge, which strongly attracts particles, which remain stuck to them. An effective handmade mask consists of two different layers: a tightly woven cotton fabric and an electrostatic fabric (natural silk or wool flannel).
(4) A mask is bad if it is not breathable: A mask that is too tightly woven, or a mask with too many layers of fabric will make it difficult for the wearer to breathe and talk, and will keep the wearer too warm. This discomfort causes the person to touch, move, or remove the mask. These actions are risky because they could bring filtered viral particles that have been deposited on the outside of the mask to your mouth, eyes, or nose and contaminate you.
A mask made of a well-filtering, breathable fabric, with a tight seal around the edges, is a good way to protect others from the large droplets you emit, as long as you always keep a safe distance!
This article observed 13 times more influenza among hospital staff using cloth masks (2-layer cotton) than among those using medical masks (FFP2 type), all other things being equal, in an excellent study in Vietnam.MacIntyre, C. R., Seale, H., Dung, T. C., Hien, N. T., Nga, P. T., Chughtai, A. A., Rahman, B., Dwyer, D. E., & Wang, Q. (2015). A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ open, 5(4), e006577
This study shows that it is indeed the electret properties of the masks that retain the particles, and that these qualities are more or less degraded by different modes of decontamination. An electret is a material with a quasi-permanent electrical polarization. By analogy, it is the equivalent of a magnet in electrostatics. Polypropylene is an electret if it is polarized by an intense electric field during its manufacture.Lin, T. H., Chen, C. C., Huang, S. H., Kuo, C. W., Lai, C. Y., & Lin, W. Y. (2017). Filter quality of electret masks in filtering 14.6-594 nm aerosol particles: Effects of five decontamination methods. PloS one, 12(10)
This article proposes a universal and reusable virus deactivation system based on a coating of fabric masks with salt. The coating simply consists in leaving the mask in a saline solution (~27g of salt for 10 cl of water) with a drop of surfactant (liquid soap) for one night and letting it dry on the radiator (not in the sun). Surgical masks treated in this way filtered 85% of the aerosols of 2.54 μm diameter containing the H1N1 virus after covering it with a salt solution. It also resulted in a 100% survival rate for the mice wearing the filter (compared to a 0% survival rate when the mice wore an uncoated mask).Quan, F., Rubino, I., Lee, S. et al. Universal and reusable virus deactivation system for respiratory protection. Sci Rep 7, 39956 (2017).
This article describes the effectiveness of masks of different fabrics in retaining particles of various diameters. It underlines the disastrous effect of leaks at the edges of the mask, and the interest of associating two different fabrics.Konda, A., Prakash, A., Moss, G. A., Schmoldt, M., Grant, G. D., & Guha, S. (2020). Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano.
Wearing well-designed fabric masks greatly reduces the remote dispersion of potentially contaminating droplets: with two layers of tightly woven cotton, no droplets are found within 10 centimeters of the mask.Rodriguez-Palacios, A., Cominelli, F., Basson, A., Pizarro, T., & Ilic, S. (2020). Textile Masks and Surface Covers - A 'Universal Droplet Reduction Model' Against Respiratory Pandemics. medRxiv.
The AFNOR S76-001 2020 "barrier masks" specification describes how to make a good mask, and how to test the tightness on the sides.Specifications in English only