Some masks do more harm than good

To combat the transmission of coronavirus, wearing the mask is today well accepted by most of us.Researchers have studied the effects of a surgical mask on the inhaled air flow and the quantities of aerosols loaded with viruses near the face and in the airways.

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Innumerable studies have shown the effectiveness of masks in the fight against the transmission of coronavirus.It is still necessary to have an effective mask, because otherwise, it is better ... Do not wear it at all, according to a new study published in Physics of Fluids.The researchers modeled the effect of a surgical mask on the inhaled air flow and the deposition of the droplets on the fabric and the face.

When we wear a mask, the air enters the mouth and nose not via a direct path, but diffuses over the entire surface of the mask at a slower speed, which promotes the penetration of droplets into the systemrespiratory.

The diffuse mask of the droplets of different sizes on the entire surface of the face and slows down the air flow, which promotes the inhalation of particles.© Jinxiang XI et al, Physics of Fluids, 2020

A defective mask leads to an increased risk

If the mask is sufficiently filtering (beyond 65 %), this does not cause a problem, but when it is worn (the filtration level can drop to 25 %), we contaminate ourselves more."Wearing a low filtration efficiency mask leads to an increased risk of deposit of ambient aerosols and can therefore do more harm than good," conclude the authors of the study.

A previous study had already shown that almost all masks, with the exception of the N95, induce a leak of suspended droplets and a risk of contamination at a distance of less than 1.8 meters.Besides, even the most filtering mask does not offer 100 % protection (it can be wet, poorly worn, etc.).He can also give a false feeling of security and lower our vigilance.

Pour en savoir plus

Coronavirus: What if the masks did more harm than good?

Article by Céline Deluzarche, published on May 6, 2020

Certains masques font plus de mal que de bien

The mask has become in public debate the central element of the deconfination.Several studies attest to its effectiveness against the transmission of SARS-COV-2.However, other scientists denounce biased conclusions and warn against the false security conferred by the port of the mask.

"If you are in good health, you should only use a mask if you take care of an alleged person infected with the COVID-19," said the World Health Organization (WHO) clearly.In other words, the mask is not recommended for the whole public."There is no evidence that wearing a mask by healthy people can prevent being infected with respiratory viruses," insists the WHO.

A position that the government has long defended, before making a voltage at 180 ° before the arguments of other scientists, until imposing the port of the mask in compulsory transport.On April 22, the Academy of Medicine called on all French people to wear without waiting for a mainstream protection mask, even artisanal, as soon as they leave their home."Be sure not to contaminate others is not optional, it is a citizen attitude which must be made compulsory in public space," burst the Academy."The port of general public mask by asymptomatic carriers, when used well used and well worn, greatly reduces the transmission of the virus," also confirms the High Council for Public Health (HCSP).

Contradictory studies are linked

In the government's discharge, it must be said that contradictory study is linked.On April 12, a South Korean study concluded that masks, including surgicals in the limitation of transmission, in particular due to the size of viral particles, capable of crossing masks.A new study by the Delve group (Data Evaluation and Learning for Viral Epidemics) of the Royal Society, based on previous research, affirms that "the general adoption of facial masks can help control the epidemic of COVVI-19By reducing the emission of droplets in the environment by asymptomatic individuals.This also confirms the experiences of the countries that have adopted this strategy, ”indicate the authors - even if most of the masks worn in Asia aim at the majority of time to protect themselves from pollution.

No solid evidence of the effectiveness of masks

"There is no solid evidence that the mask can reduce the transmission of the virus to the community," rejects Ben Killingley, consultant in acute medicine and infectious diseases at the University College hospital in London, interviewed by the Guardian."Studies on facial masks have not been carried out during a pandemic or in the context of a new virus," warns the specialist.In addition, the tests are carried out in the laboratory, far from the real conditions of everyday life.

The discomfort caused by the mask leads people to touch their face more frequently.© Africa Studio, Adobe Stock

However, according to several specialists, the disadvantages of masks largely prevail over its profits."The use of large -scale medical masks can create a false feeling of safety, and cause the negligence of other essential measures, such as hand hygiene and physical distancing", notes for example WHO.

Secondly, the discomfort caused by the mask leads people to touch their face more frequently with their potentially contaminated hands, which increases the risk of catching the virus.Not to mention the difficulties in breathing through certain masks.In fact, we see a large number of people who claimed horn and crising masks carry the masks ... on the chin."I am allergic to the fabric", pleads for example Sophie, cashier in Strasbourg.Last concern: the mask must in principle be washed after each use, which is far from being the case.

The precautionary principle before scientific evidence?

"Before implementing public interventions involving billions of people, we need randomized controlled trials at the level of the population or at least monitoring by observation with comparison groups," concludes Antonio Lazzarino, from the department of'Epidemiology and public health of the University College of London.Precautions that the government did not expect to order 3 billion masks and to extend its distribution to supermarkets.

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Liens externesEffects of mask-wearing on the inhalability and deposition of airborne SARS-CoV-2 aerosols in human upper airwayFace Masks for the General PublicReport on face masks' effectiveness for Covid-19 divides scientistsCommuniqué de l’Académie nationale de MédecineDéfinitions associéesVoLTE, c'est quoi ?Qu'est-ce que Twitter ?

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