Stinging clouds of tear gas explode beneath a car full of children, forcing them to flee into the snowy street for clean air to breathe. A man, his face painted orange with pepper spray, is pinned to the icy ground by masked federal agents, unable to erase the pain from his burning eyes. For weeks, reports of such incidents have been coming from Minnesota, where the Department of Homeland Security is facing daily protests over the largest immigration enforcement operation the agency has conducted in its history.
DHS says it has arrested thousands of undocumented immigrants and Homeland Security Secretary Kristi Noem justified the widespread use of tear gas and pepper spray, even though visual evidence shows officers deploying the chemicals largely against peaceful protesters and bystanders. These chemicals are banned in wartime by international treaties, but they have been used by U.S. law enforcement against civilians for decades.
While it is clear that these “crowd control agents” are designed to cause an immediate and debilitating response, health experts have expressed serious concerns about their lasting effects on the body.
“These are chemical weapons that are harmful to the human body and to particularly vulnerable people, 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, much more serious things,” she says, even death.
But the long-term health risks are poorly understood. No large systematic studies have investigated health problems that emerge long after exposure to these chemicals, says Anthony Szema, chair of the American Thoracic Society’s Section on Inhalation Terrorism and Disasters. Some research, however, has painted a picture of lasting impacts. For weeks or even months after immediate exposure, crowd control agents can continue to sabotage the organs that allow us to breathe, pump blood, and even create 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 encompass a multitude of chemicals.
U.S. law enforcement has used tear gas against civilians for more than a century. The compound 2-chlorobenzalmalononitrile, or CS, is the most commonly used tear gas irritant today. It is usually deployed via explosive gas canisters and sometimes mixed with jets fired from water cannons.
Pepper spray typically contains oleoresin capsicum (OC), a resinous blend of chili pepper extracts that includes capsaicin and whose use became popular in the 1960s. It can be particularly harmful to people with pepper allergies, says Szema, a pulmonologist at Hofstra University in Hempstead, New York. Alternatively, pepper spray may contain PAVA, which contains a lab-made version of OC. These chemicals are often sprayed from hand-held canisters, and they are also found in pepper balls, paintball-like projectiles fired from specialized weapons.
It’s an overview. But one of the major problems with studying compounds for crowd control is that it is often difficult to know which chemicals are used and at what concentrations. There are no national regulations regarding these chemical agents, and manufacturers share very little information about what’s in them, says Rohini Haar, an emergency physician and epidemiologist at the University of California, Berkeley. This means it’s not always clear what’s in the vapors escaping from a tear gas canister, which can make it difficult to link the use of specific chemicals to specific health risks.
Although it seems very likely that the tear gas 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 they’re made, but there are no regulations to tell us what people are buying or what’s in a can.”
The picture is further muddied by other compounds that are mixed to facilitate dispersion or prolong exposure, and which may themselves be toxic. For example, tear gas canisters may contain potassium perchlorate, a chemical that provides oxygen when the canister explodes and has also been linked to thyroid problems. And CS is sometimes mixed with silica gel to keep it from disintegrating quickly. These longer-lasting forms can linger on clothing 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 eyes and in our airways, says Sven Jordt, a pain and sensation researcher at Duke University. This immediately triggers protective reflexes – coughing, tears, mucus secretion – which help eliminate the chemicals. “But these agents are so powerful that these reflexes become overwhelming, and [they] you will incapacitate yourself if you don’t remove yourself from the situation,” Jordt says.
There is no antidote for these agents, says the U.S. Centers for Disease Control and Prevention. If a person is exposed, they should move away from the source of exposure, find fresh air, wash their skin with soap and water, and rinse their eyes until they appear free of chemicals, the CDC recommends. After following these steps, you usually need to about 30 minutes for symptoms to go away, although more severe exposure may result in lasting symptoms, especially if the person was exposed indoors.
Children are among the most exposed to these chemicals, due to their small size 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,” says Jordt. “Their airways are smaller in diameter, so if there’s an obstruction, swelling or mucus, they have a harder time breathing.” Additionally, CS gas tends to accumulate near the ground and children are smaller, potentially increasing their exposure, he says.
Longer-term respiratory risks
Acute symptoms have been well documented. But the long-term effects of crowd control agents remain poorly understood. Much of what is known is based on anecdotal evidence, such as reports from conflict zones, Hassan says. And many studies have only looked at healthy populations, like military recruits, and are not representative of the population as a whole, Jordt says.
But even studies on healthy groups are concerning.
A 2014 study of more than 6,000 army recruits found that the chances of being diagnosed with an acute respiratory illness – such as bronchitis, sinusitis and sore throat – more than doubled after exposure to tear gas during basic training. A total of 114 recruits were diagnosed with respiratory illness in the week following exposure to the CS agent, while 47 were diagnosed the week before.
The study also found that higher exposure levels were associated with greater disease risks, and subsequent research found that reducing exposure concentrations reduces risks. This research showed that the effects of tear gas persisted into the days following exposure in healthy subjects, leading the military to limit concentrations and exposure times and improve decontamination procedures, Jordt says.
These chemicals, especially the CS agent, can burn the surface of the eyes and respiratory tract, damaging the lining of the respiratory system and the eye for a period of time, says Jordt. This can cause fluid to leak into the lungs, causing pulmonary edema, which can then lead to infection and other breathing problems. After high levels or repeated exposures, this type of damage can potentially have lasting effects.
Older adults, smokers, and people with asthma or other respiratory problems should be especially wary of exposure, Jordt says, because the chemicals could trigger or exacerbate preexisting respiratory problems, including infectious diseases. That’s a concern for Minnesotans because the protests are taking place during the height of respiratory virus season, Szema points out.
Other studies have also linked respiratory diseases And exposure to tear gas. For example, in a 2017 report reviewed by the Human Rights Center at UC Berkeley, Haar and psychologist Jess Ghannam of the University of California, San Francisco, described experiences of people exposed to tear gas almost daily in the camps in the West Bank. “The long-term impacts have been, you know, catastrophic, like lung problems, asthma, respiratory problems, skin allergies,” Haar says. This level of daily exposure over years and in crowded conditions can be extreme, but it can provide insight into places like Portland, Chicago, and Minnesota, where civilians were repeatedly exposed to tear gas and pepper spray by law enforcement.
Persistent heart problems
Although the risks of respiratory problems seem somewhat intuitive, evidence suggests that the effects may spread beyond the depths of breathing. In 2025, a group of researchers led by pediatrician Konstantine Chakhunashvili of Caucasus University in Tbilisi, Georgia, reported rate significant heart problems among demonstrators who were teargassed during demonstrations against the results of the 2024 Georgian parliamentary elections.
Chakhunashvili and his colleagues observed the hearts of 69 protesters who had been exposed to tear gas during the protests, where canisters containing the CS agent were found. Ultrasound examinations of the subjects’ hearts, taken at least five weeks after exposure, revealed delayed electrical impulses in the hearts of about a third of the protesters and in only 7 percent of unexposed individuals. The researchers also detected a signal often associated with decreased blood flow in the hearts of about 29 percent of protesters and in 3 percent of unexposed people.
This suggests there is a link between tear gas and “possible problems with blood oxygenation and possible oxygen deprivation of a heart muscle” that can persist for weeks, Chakhunashvili says. He and his colleagues also surveyed more than 300 protesters 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 their exposure.
Further studies are needed to determine cause and effect. Nevertheless, “the indiscriminate nature of tear gas should at least encourage the democratic world to put in place stricter rules regarding their use,” he says.
Reproductive implications
Researchers in Minneapolis have expressed concern about the lingering effects of tear gas on another part of the body. Hassan was living in south Minneapolis in 2020 when protests erupted against the murder of George Floyd – an unarmed black man – by a police officer. “My neighbors told me they were experiencing unexpected changes in their bodies,” she says.
People who had not had their periods in years, due to birth control or hormone use, told Hassan that they experienced spontaneous menstrual bleeding moments after being exposed to tear gas. “Hearing that like once, I don’t know, maybe it sounds like a fluke,” Hassan says. “I have heard this many times from my neighbors and community members.”
Hassan and his colleagues analyzed responses to a survey of more than 1,200 people who had been exposed to chemical agents by law enforcement in 2020 and 2021. In 2023, Hassan and his colleagues reported that 83% of those exposed felt uterine cramps, breast tenderness, or early or late menstrual bleeding. Additionally, they found that people exposed for more than two days were twice as likely to experience an adverse effect as those exposed for just one day.
Notably, 10 of the 19 people who reported they were pregnant at the time of exposure reported a subsequent miscarriage, about twice the expected miscarriage rate. Although the sample size was too small to conclusively associate exposure and miscarriage, the findings raise questions about the short- and long-term fertility of those exposed to crowd control chemicals, Hassan and colleagues note in the study.
83
percent
— percentage of more than 1,200 people exposed to chemical crowd control agents who experienced uterine cramps, breast tenderness and menstrual irregularities.
This is not the first time that such a link has been mentioned. For example, Haar’s work in the West Bank and a 2012 report on the use of tear gas against civilians in the West Bank. Bahrain both noted miscarriages following exposure. And in 2011, concerns about this link prompted the Chilean government to ban tear gas, but 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 someone to suddenly have spontaneous bleeding after years,” she says. Another explanation is that these agents disrupt our body’s hormonal systems, say Hassan and Jordt: in the same way as BPA plastic compound.
Today, Hassan is collecting data to determine whether the widespread use of tear gas in Minneapolis affected preterm birth rates in 2020 and 2021 and may also include data from 2025 and 2026 as soon as it becomes available. “I was repeatedly receiving emails from health care providers who had noticed more premature births,” she says. “I hope to be able to explore that a little bit and understand if there are any changes at the population level.”
Research efforts like Hassan’s are rare in the United States, due to a lack of federal support for research — a drought that set in long before DHS began operations in Minnesota. There is virtually no government funding for this type of research, Haar and Jordt say. “It seems to me that the government has no real, serious intention of trying to understand the health effects of these agents,” Jordt says.
