Tear gas and pepper spray can have lasting health effects

Stinging clouds of tear gas explode from beneath a car full of children, forcing them to flee into the snowy street to seek air that’s safe to breathe. A man, face painted orange with pepper spray, is pinned to the icy ground by masked federal agents, unable to wipe the pain from his burning eyes. For weeks, reports of incidents like these have been coming out of Minnesota, where the Department of Homeland Security is facing daily protests over the agency’s largest immigration enforcement operation in its history.

DHS claims it has arrested thousands of undocumented immigrants, and Secretary of Homeland Security Kristi Noem has justified the widespread use of tear gas and pepper spray, even though visual evidence shows agents deploying the chemicals largely against peaceful protesters and bystanders. These chemicals are banned in warfare by international treaties, but they have been used by U.S. law enforcement against civilians for decades.

While it’s clear these “crowd control agents” are designed to cause an immediate, debilitating reaction, health experts have raised serious concerns about their enduring effects on the body.

“These are chemical weapons that are harmful to the human body and harmful to particularly vulnerable folks, like children,” says Asha Hassan, an epidemiologist at the University of Minnesota in Minneapolis. “We know that tear gas causes tears, but it also causes other things that are a lot more severe,” she says — even death.

But the long-term health risks are poorly understood. No large, systematic studies have investigated the health problems that emerge long after exposure to these chemicals, says Anthony Szema, chair of the American Thoracic Society’s Section on Terrorism and Inhalation Disasters. Some research, though, has painted a picture of enduring repercussions. For weeks and even months after the immediate moments of exposure, crowd control agents can continue to sabotage the organs that allow us to breathe, pump blood and even make life.

Here’s a closer look at these chemicals and what’s known about their immediate and long-term health impacts.

What’s in crowd control agents

Tear gas and pepper spray are vague terms that encapsulate a slew of chemicals.

Tear gas has been used by U.S. law enforcement against civilians for over a century. The compound 2-chlorobenzalmalononitrile, or CS, is the most common tear gas irritant used today. It is commonly deployed via exploding gas canisters and sometimes mixed into jets shot from water cannons.

Pepper spray typically contains oleoresin capsicum (OC), a resinous mixture of chili pepper extracts that includes capsaicin and became popular for use in the 1960s. It can be particularly harmful to people with allergies to peppers, says Szema, a pulmonologist at Hofstra University in Hempstead, N.Y. Alternatively, pepper spray can contain PAVA, which contains a lab-made version of OC. These chemicals are often sprayed from handheld canisters, and they’re also found in pepperballs — paintball-like projectiles fired from specialized guns.

That’s a big-picture look. But a major problem with studying crowd control compounds is that it’s often unclear which chemicals are being used and in what concentrations. There is no national level regulation of these chemical agents, and manufacturers share very little information about what goes into them, says emergency physician and epidemiologist Rohini Haar of the University of California, Berkeley. That means it’s not always clear what’s in the fumes that spew from a tear gas cannister, and that can make it difficult to tie the use of specific chemicals to specific health risks.

While it seems most probable that the tear gas being used in Minneapolis contains CS, law enforcement also has access to even more painful but less studied versions of CS, called CX and CR, Haar says. “I know they exist, I know that they’re manufactured, but there’s no regulation on telling us what people are buying or what’s in a canister.”

Further muddying the picture are the other compounds that get mixed in to assist with dispersal or prolong exposure, and which can be toxic themselves. For instance, tear gas cannisters may contain potassium perchlorate, a chemical that donates oxygen to the cannister’s explosion and which has also been linked to thyroid issues. And CS is sometimes mixed with silica gel to keep it from disintegrating quickly. These longer-lasting forms can linger on clothes and expose first responders, and they can affect an area for days.

First comes the pain

Tear gas and pepper spray activate pain-sensing nerves on the skin, on the surface of the eye and in our airways, says Sven Jordt, a pain and sensation researcher at Duke University. That immediately triggers protective reflexes — coughing, tears, mucus secretion — that help wash away the chemicals. “But these agents are so potent that these reflexes become overwhelming, and [they] incapacitate you if you don’t remove yourself from the situation,” Jordt says.

There is no antidote for these agents, the U.S. Centers for Disease Control and Prevention says. If a person is exposed, they should move away from the exposure source, find fresh air, wash their skin with soap and water and rinse their eyes until they appear clear of chemicals, the CDC recommends. After following those steps, it typically takes about 30 minutes for symptoms to disappear, though more severe exposure may lead to long-lasting symptoms, especially if the individual was exposed indoors.

Children are among the most at risk from these chemicals, due to their small bodies and the vulnerability of their pain nerves. “Their tissues are more delicate, their skin is thinner, so it’s easier for the agent to reach their nerve endings,” Jordt says. “Their airways have a smaller diameter, so if there’s any obstruction, swelling, mucus, they have more trouble breathing.” Moreover, CS gas tends to accumulate near the ground, and children are shorter, which potentially increases their exposure, he says.

Longer-term respiratory risks

Acute symptoms have been well-documented. But the longer-term effects of crowd control agents remain poorly understood. Much of what’s known is based on anecdotal evidence, such as reports from conflict zones, Hassan says. And many of the studies looked only at healthy populations like military recruits, and aren’t representative of the broader population, Jordt says.

But even studies on healthy groups have been concerning.

A 2014 study of more than 6,000 army recruits found the odds of being diagnosed with an acute respiratory illness — such as bronchitis, sinusitis and throat pain — more than doubled after exposure to tear gas in basic training. A total of 114 recruits were diagnosed with respiratory illness during the week following exposure to the CS agent, while 47 were diagnosed in the week before.

The study also found that higher amounts of exposure were associated with greater chances of illness, and subsequent research found that reducing exposure concentrations reduced the risks. That research showed that the effects of tear gas persisted in the days following exposure in healthy subjects, and it led the military to limit exposure concentrations and durations and improve decontamination procedures, Jordt says.

These chemicals, especially the CS agent, can burn the surfaces of the eyes and the airways, damaging the lining of the respiratory system and the eye for some time, Jordt says. That can lead to fluids leaking into the lungs, causing pulmonary edema, which can subsequently lead to infection and other respiratory issues. After high levels or repeated instances of exposure, that sort of damage may potentially cause lasting effects.

The elderly, smokers and people with asthma or other respiratory conditions should be especially wary about exposure, Jordt says, as the chemicals could trigger or exacerbate preexisting respiratory issues, including infectious diseases. That’s a concern for the people in Minnesota because the protests are occurring in the middle of respiratory virus season, Szema points out.

Other studies have also linked respiratory illnesses and tear gas exposure. For instance, in a 2017 report reviewed by UC Berkeley’s Human Rights Center, Haar and psychologist Jess Ghannam of the University of California, San Francisco described experiences of people exposed to tear gas almost daily in camps in the West Bank. “The long-term impacts were, you know, catastrophic, like lung problems, asthma, breathing issues, skin allergies,” Haar says. That level of daily exposure over years and in crowded conditions may be extreme, but it can provide insights into places like Portland, Chicago and Minnesota, where civilians have been repeatedly exposed to tear gas and pepper spray by law enforcement.

Lingering heart problems

While the risks of respiratory issues seem somewhat intuitive, evidence suggests that effects can cascade beyond the depths of one’s breath. In 2025, a group of researchers led by pediatrician Konstantine Chakhunashvili of the Caucasus University in Tbilisi, Georgia, reported significant rates of heart issues in demonstrators who had been teargassed during the protests over Georgia’s 2024 parliamentary election results.

Chakhunashvili and his colleagues observed the hearts of 69 demonstrators who had been exposed to tear gas at the protests, where canisters containing the CS agent were found. Ultrasound examinations of subjects’ hearts — which were conducted at least five weeks after exposure — revealed delayed electrical impulses in the hearts of about a third of the demonstrators and in just 7 percent of nonexposed individuals. The researchers also detected a signal often associated with reduced blood flow in the hearts of about 29 percent of the demonstrators, and in 3 percent of the unexposed people.

That suggests there’s a link between tear gas and “possible issues with oxygenation of blood and possible oxygen deprivation of a heart muscle” that can linger for weeks, Chakhunashvili says. He and his colleagues also surveyed over 300 demonstrators and found that more than a third reported experiencing headaches, eye problems, skin disorders, high blood pressure or psychological trauma more than a month after exposure.

More studies are needed to determine cause and effect. Nonetheless, “the indiscriminate nature of tear gas should prompt at least the democratic world to implement stricter rules about its use,” he says.

Reproductive repercussions

Researchers in Minneapolis have raised concerns that tear gas might have lingering impacts on another part of the body. Hassan was living in southern Minneapolis in 2020 when protests erupted over the killing of George Floyd — an unarmed Black man — by a police officer. “I was hearing … from my neighbors that they were experiencing unexpected changes in their bodies,” she says.

Individuals who had not experienced menstruation in years, due to birth control or hormone use, told Hassan that they experienced spontaneous menstrual bleeding in the moments after being exposed to tear gas. “Hearing that like one time, I don’t know, maybe sounds like a fluke,” Hassan says. “I heard that several times from my neighbors and community members.”

Hassan and her colleagues analyzed survey responses from more than 1,200 people who had been exposed to chemical agents by law enforcement in 2020 and 2021. In 2023, Hassan and her colleagues reported that 83 percent of the exposed individuals experienced uterine cramping, breast tenderness or early or late menstrual bleedings. What’s more, they found that individuals that had been exposed on more than two days were twice as likely to experience an adverse effect as those exposed on one day.

Notably, 10 of the 19 individuals who reported that they were pregnant when exposed reported a subsequent miscarriage — that’s about twice the expected rate of miscarriage. Though the sample size is too small to conclusively associate exposure and miscarriage, the finding raises questions about both the short- and long-term fertility of those who are exposed to crowd control chemicals, Hassan and her colleagues note in the study.

It’s not the first time such a link has been brought up. For instance, Haar’s work in the West Bank and a 2012 report on teargassing of civilians in Bahrain both noted miscarriages following exposure. And in 2011, concerns about the link prompted the government of Chile to ban tear gas, though only temporarily.

One hypothesis is that stress is at least partly to blame, Jordt says. Hassan, however, suspects a more physical explanation. “It would take a lot [of stress] for somebody to all of a sudden have a spontaneous bleed after years,” she says. Another explanation is that these agents are disrupting hormonal systems in our bodies, both Hassan and Jordt say, similarly to how the plastics compound BPA does.

Now, Hassan is collecting data to investigate whether widespread tear gas use in Minneapolis affected preterm birth rates in 2020 and 2021 and may also include data from 2025 and 2026 as it becomes available. “I repeatedly was getting emails from health care providers who had noticed more preterm birth,” she says. “I’m hoping to be able to explore that a little bit and get an understanding if there are population level changes.”

Research efforts like Hassan’s are uncommon in the United States, due to a scarcity of federal research support — a drought that had set in long before DHS began its operation in Minnesota. There’s basically no government funding for this sort of research, Haar and Jordt say. “It seems to me that there is no real, serious intent to try and understand the health effects of these agents from the side of the government,” Jordt says.