Protests against racism and police brutality, triggered by the tragic killing of George Floyd at the hands of a Minneapolis police officer, have emerged in every major American city and in countries around the world. In many places, the protestors have been met with heavy resistance from police wielding tear gas—a chemical weapon that dates back to the early 20th century.

What is tear gas?

Tear gas isn’t one specific chemical and, despite the name, it’s usually not even a gas. There are a few different compounds that are used as “lachrymatory agents.” Most of them are solids at room temperature, and get mixed with liquid or gas dispersal agents for use.

Where did tear gas come from?

Tear gases are something that militaries have been messing around with since World War I. Both France and Germany developed and deployed lachrymatory irritants in battle, but there was evidently a bit of a learning curve. According to the U.S. Army’s Combat Studies Institute, the Germans fired some 3000 tear gas shells during one day of fighting in 1914, but the British troops on the receiving end “suffered no ill effects and never suspected they were under chemical attack.”

Shortly thereafter, the Germans had gotten a better handle on things and were using tear-inducing gases to great effect. In 1916, they fired 2000 shells into a French trench system and 2400 French soldiers—blinded, coughing, and crying—quickly found themselves surrounded by German troops in protective goggles.

CS gas would come a few decades later. Its active component, 2-chlorobenzylidene malononitrile, was synthesized by American chemists Ben Corson and Roger Stoughton in 1928 (the CS stands for Corson and Stoughton). Tear gas using it was developed and tested during the 1950s and '60s.

What does tear gas do?

Tear gases irritate the mucous membranes of the eyes, nose, mouth, and lungs, and cause tearing, coughing, burning, and stinging sensations; chest tightness, and difficulty breathing. At higher concentrations, exposure can cause stomach irritation leading to vomiting and diarrhea.

According to German toxicologist Uwe Heinrich, dispersing the gas at a concentration of 1 mg per cubic meter will cause symptoms of irritation. From there, things go sour pretty quickly. A concentration of 10 mg per cubic meter can force trained soldiers to retreat from an area. Ten to 20 mg/m3 or higher can cause serious injury or, depending on the victim and conditions of exposure, death. In one incident reported in a Swiss medical journal, an otherwise healthy adult man was exposed to a tear gas grenade containing just one gram of CS while inside a building. He quickly developed toxic pulmonary edema, a condition where excess fluid collects in the air sacs of the lungs and causes difficulty breathing, and recovered only after weeks of medical treatment.

Being hit with tear gas may make you more susceptible to respiratory illness, like influenza or COVID-19, later on, Duke University anesthesiology professor Sven-Eric Jordt tells OneZero. Prolonged exposure to tear gas in an enclosed setting can cause long-term injuries, including glaucoma, blindness, respiratory failure, and even death.

And, because tear gas is actually a solid, its particles can coat any surface they fall on, such as clothing, food, animals, and plants. The extent of environmental damage associated with tear gas is not well studied, but the chemical likely contributes to air pollution as well. It may further burden Black and Latino communities disproportionately saddled with environmental pollution.

Shouldn’t tear gas be illegal?

It is, kind of. Tear gases were used in warfare throughout most of the 20th century until 1993, when the Chemical Weapons Convention banned the production, stockpiling, and use of chemical weapons in battle. The international treaty doesn’t apply to nations’ domestic law enforcement, though, so police officers in the United States are free to spray it at civilians, typically as a means of crowd dispersal.

How do you treat tear gas exposure?

If you’re outside, the best antidote to any breathing problems is fresh, untainted air, and time. For high-dose exposure or exposure in enclosed spaces, bottled oxygen or certain asthma medications may be administered to ease difficulty breathing. Any exposed skin should be washed with soap and water and eyes should be flushed with sterile water or saline solution. Some protestors use a solution of baking soda and water on the theory that the basic sodium bicarbonate can weaken the molecules in tear gas and counteract its effects. Others have used milk or milk of magnesia to fight the burning sensation in pepper spray; experts caution that these fluids aren't sterile and could cause infection.

This story has been updated for 2020.