According to the Centers for Disease Control and Prevention: “Riot control agents (sometimes referred to as “tear gas”) are chemical compounds that temporarily make people unable to function by causing irritation to the eyes, mouth, throat, lungs, and skin.”

And, according to the CDC, “several different compounds” fall under this definition, and are employed by security forces, including military and police, in riot control situations.

Among others, they include chloroacetophenone (CN), more commonly referred to as “mace,” or pepper sprays — in other words, the compound that was deployed in Lafayette Square — and chlorobenzylidenemalononitrile (CS), “one of the most commonly used tear gases in the world,” according to an article in the British Medical Journal.

These compounds are all typically referred to as “tear gas” because their most prominent effect is to bring on tears.