Your mother was right: when you cough or sneeze, your germs carry -- but farther than likely you or she ever imagined.

A unique study by researchers at the Massachusetts Institute of Technology, or MIT, shows when people cough and sneeze, they expel gas clouds that keep their potentially infectious droplets gliding through the air a lot longer, and for much greater distances than previously thought.

Try 200 times as far, says a new paper published in the April issue of the Journal of Fluid Mechanics.

"When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you," John Bush, a professor of applied mathematics at MIT and co-author of the new paper, said in a news release. "But you don't see the cloud, the invisible gas phase. The influence of this gas cloud is to extend the range of the individual droplets, particularly the small ones."

The research revealed the smaller droplets that emerge in a cough or sneeze may travel as far as 200 times the distance they would have if they moved as groups of unconnected particles, which previous work assumed they did.

But, the newly-realized tendency of the droplets to remain airborne, re-suspended by gas clouds, means there's a much greater risk ventilation systems can transmit potentially infectious particles.

Therefore, said the MIT research team, in order to reduce the potential transmission of airborne pathogens, architects and engineers may want to re-examine the design schematics of workplaces and hospitals, along with the air circulation systems on airplanes.

"You can have ventilation contamination in a much more direct way than we would have expected originally," said Lydia Bourouiba, also a study co-author and an assistant professor in MIT's Department of Civil and Environmental Engineering.

The researchers used high-speed imaging of coughs and sneezes, along with laboratory simulations and mathematical modeling, to produce a new analysis of from a fluid-mechanics perspective.

Their conclusions prove the world of bodily expulsions is very different from what traditional scientific reasoning predicted.

For instance, prior to the study, researchers thought larger mucus droplets fly farther than smaller ones because, abiding by the classic definition of mass multiplied by velocity, they have more momentum.

However, all that is based on the assumption each droplet isn't connected to the others around it.

The latest experimentation helped illustrate the interactions of expelled droplets with the accompanying gas cloud can multiply their hang times dramatically.

"By elucidating the dynamics of the gas cloud, we have shown that there's a circulation within the cloud -- the smaller drops can be swept around and re-suspended by the eddies within a cloud, and so settle more slowly," Bush said. "Basically, small drops can be carried a great distance by this gas cloud while the larger drops fall out. So you have a reversal in the dependence of range on size."

A cough or sneeze, said the study, is a "multiphase turbulent buoyant cloud," because the cloud mixes with surrounding air before its load of liquid droplets falls out, evaporates into solid residues, or both.

"The cloud entrains ambient air into it and continues to grow and mix ... But as the cloud grows, it slows down, and so is less able to suspend the droplets within it," Bourouiba said.

"You thus," she added, "cannot model this as isolated droplets moving ballistically."