Repeated coughing seriously degrades face mask efficiency

June 16, 2020

WASHINGTON, June 16, 2020 -- Face masks are thought to slow the spread of viruses, including the novel coronavirus that causes COVID-19, but little is known about how well they work.

In an issue of Physics of Fluids, by AIP Publishing, Talib Dbouk and Dimitris Drikakis, from the University of Nicosia in Cyprus, use precise computer models to map out the expected flow patterns of small droplets released when a mask-wearing person coughs repeatedly.

Previous work from this research group showed droplets of saliva can travel 18 feet in five seconds when an unmasked person coughs. This new work used an extended model to consider the effect of face masks and multiple cycles of coughing.

The results show masks can reduce airborne droplet transmission. However, the filtering efficiency of masks is adversely affected by repeated coughing, as might happen when an individual is ill. Repeated coughs reduce the efficiency, letting many more droplets through.

The model was created using complex mathematical equations for turbulence and other flow effects. A sequence of coughs was modeled by applying several cycles of forward-directed velocity pulses to the initial droplets. The researchers performed numerical simulations that account for droplet interactions with the porous filter in a surgical mask.

The results are alarming. Even when a mask is worn, some droplets can travel a considerable distance, up to 1 meter, during periods of mild coughing. Without a mask, droplets travel twice as far, however, so wearing a mask will help. A mask also decreases the number of droplets that leak out the side of the mask but fails to eliminate it entirely.

These calculations also revealed an effect on the droplet size due to turbulent flow encountering the mask, escaping and entering the environment.

"The droplet sizes change and fluctuate continuously during cough cycles as a result of several interactions with the mask and face," said Drikakis.

Dbouk explained how droplet sizes might change. "Masks decrease the droplet accumulation during repeated cough cycles," Dbouk said. "However, it remains unclear whether large droplets or small ones are more infectious."

"The use of a mask will not provide complete protection," Drikakis said. "Therefore, social distancing remains essential." For health care workers, the investigators recommend much more complete personal protective equipment, including helmets with built-in air filters, face shields, disposable gowns and double sets of gloves.

The investigators also urge manufacturers and regulatory authorities to consider new criteria for assessing mask performance that account for flow physics and cough dynamics. They also proposed a new criterion for mask performance assessment.
The article, "On respiratory droplets and face masks," is authored by Talib Dbouk and Dimitris Drikakis. The article will appear in Physics of Fluids on June 16, 2020 (DOI: 10.1063/5.0015044). After that date, it can be accessed at


Physics of Fluids is devoted to the publication of original theoretical, computational, and experimental contributions to the dynamics of gases, liquids, and complex fluids. See

American Institute of Physics

Related Physics Articles from Brightsurf:

Helium, a little atom for big physics
Helium is the simplest multi-body atom. Its energy levels can be calculated with extremely high precision only relying on a few fundamental physical constants and the quantum electrodynamics (QED) theory.

Hyperbolic metamaterials exhibit 2T physics
According to Igor Smolyaninov of the University of Maryland, ''One of the more unusual applications of metamaterials was a theoretical proposal to construct a physical system that would exhibit two-time physics behavior on small scales.''

Challenges and opportunities for women in physics
Women in the United States hold fewer than 25% of bachelor's degrees, 20% of doctoral degrees and 19% of faculty positions in physics.

Indeterminist physics for an open world
Classical physics is characterized by the equations describing the world.

Leptons help in tracking new physics
Electrons with 'colleagues' -- other leptons - are one of many products of collisions observed in the LHCb experiment at the Large Hadron Collider.

Has physics ever been deterministic?
Researchers from the Austrian Academy of Sciences, the University of Vienna and the University of Geneva, have proposed a new interpretation of classical physics without real numbers.

Twisted physics
A new study in the journal Nature shows that superconductivity in bilayer graphene can be turned on or off with a small voltage change, increasing its usefulness for electronic devices.

Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.

2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'

Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.

Read More: Physics News and Physics Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to