Sven-Eric Jordt, a researcher at Duke University who has studied the effects of tear gas agents, said he had been shocked to watch how much the authorities had turned to the control method in recent days…

In research conducted by the U.S. Army, examiners looked at the impacts of exposure that thousands of Army recruits had to the common riot-control agent known as CS gas or tear gas. The study conducted in the summer of 2012 found that the personnel in a basic training cohort had a substantially high risk of being found to have an acute respiratory illness in the days after exposure than the days before.

The risk increased the more people were exposed, the researchers said.