Before the tearing, the choking and the pouring mucus, tear gas burns. It causes searing pain in the eyes, skin, lungs and mouth—or anywhere it touches. “It can be overwhelming and incapacitating.

You can be forced to shut your eyes and cannot open them,” says Sven-Eric Jordt, an anesthesiologist at Duke University. And then comes the coughing and the nausea and the vomiting. What causes these chemicals to have such devastating effects on the human body?

Read more at PBS News.