Pungent clouds of irritant gas burst from under a vehicle carrying youngsters, compelling them to escape into the wintry thoroughfare in search of breathable atmosphere. A fellow, visage daubed in orange from defensive spray, is pinned to the frozen terrain by uniformed federal officers, unable to alleviate the torment from his burning vision. For weeks, accounts of such occurrences have emerged from Minnesota, where the Department of Homeland Security is confronting daily demonstrations against the administration’s most extensive immigration enforcement initiative ever undertaken.
DHS asserts it has apprehended numerous undocumented individuals, and Secretary of Homeland Security Kristi Noem has defended the widespread deployment of tear gas and pepper spray, despite visual evidence indicating agents directing these substances predominantly against non-violent demonstrators and onlookers. These compounds are prohibited in armed conflict by global accords, yet they have been utilized by U.S. law enforcement against civilians for many years.
While it is evident that these “riot control agents” are formulated to provoke an immediate, disabling response, medical professionals have voiced significant apprehension regarding their lasting consequences on the human body.
“These are noxious agents detrimental to the human organism and particularly harmful to susceptible individuals, such as children,” states Asha Hassan, an epidemiologist affiliated with the University of Minnesota in Minneapolis. “We are aware that tear gas induces lacrimation, but it also precipitates other, far more serious, ailments,” she remarks, even suggesting fatality.
However, the protracted health hazards remain largely unexamined. No extensive, systematic investigations have explored the medical issues that manifest long after exposure to these substances, according to Anthony Szema, chairperson of the American Thoracic Society’s Section on Terrorism and Inhalation Disasters. Nevertheless, some research has illuminated the potential for enduring repercussions. For weeks, and sometimes months, following the initial moments of exposure, riot control agents can continue to impair the vital organs responsible for respiration, circulation, and even procreation.
Herein lies a more detailed examination of these compounds and the current understanding of their immediate and lasting health ramifications.
Composition of Riot Control Agents
Tear gas and pepper spray are broad designations that encompass a variety of chemical agents.
Tear gas has been employed by U.S. law enforcement against the populace for over a century. The chemical 2-chlorobenzalmalononitrile, or CS, is the most prevalent tear gas irritant in contemporary use. It is typically dispersed via exploding ordnance or occasionally mixed into streams expelled from water cannons.
Pepper spray generally contains oleoresin capsicum (OC), a resinous extract derived from chili peppers that includes capsaicin and gained popularity in the 1960s. It can pose a particular risk to individuals with chili pepper allergies, notes Szema, a pulmonologist at Hofstra University in Hempstead, N.Y. Alternatively, pepper spray may incorporate PAVA, a synthetic analogue of OC. These agents are frequently discharged from handheld devices and are also incorporated into pepperballs—projectiles resembling paintballs fired from specialized weaponry.
This provides a general overview. However, a significant challenge in studying riot control compounds stems from the frequent ambiguity regarding the specific chemicals employed and their concentrations. There is no nationwide regulation governing these chemical agents, and manufacturers disclose minimal information about their ingredients, according to Rohini Haar, an emergency physician and epidemiologist at the University of California, Berkeley. Consequently, it is not always clear what substances are present in the fumes emanating from a tear gas canister, which can complicate efforts to link the use of particular chemicals to specific health risks.
While it is highly probable that the tear gas deployed in Minneapolis contains CS, law enforcement also has access to more potent yet less investigated variants of CS, designated CX and CR, Haar states. “I am aware of their existence and manufacture, but there is no regulatory oversight indicating what quantities are procured or what is contained within a canister.”
Further obscuring the situation are additional compounds incorporated to facilitate dispersal or prolong the effects, some of which can be toxic in their own right. For instance, tear gas canisters may contain potassium perchlorate, a substance that supplies oxygen for the canister’s detonation and has also been associated with thyroid dysfunctions. Furthermore, CS is occasionally combined with silica gel to retard its degradation. These prolonged-acting formulations can adhere to clothing, exposing first responders, and may contaminate an area for several days.
Initial Discomfort and Pain
Tear gas and pepper spray activate nociceptors located on the skin, ocular surfaces, and within the respiratory passages, explains Sven Jordt, a researcher specializing in pain and sensation at Duke University. This promptly initiates protective responses—coughing, lacrimation, and mucus production—designed to expel the irritants. “However, these agents are so potent that these reflexes become overpowering, incapacitating individuals if they do not remove themselves from the environment,” Jordt elaborates.
There is no known antidote for these agents, according to the U.S. Centers for Disease Control and Prevention. In instances of exposure, individuals are advised to withdraw from the source of the irritant, seek fresh air, cleanse their skin with soap and water, and irrigate their eyes until all chemical residue is visibly absent, as recommended by the CDC. Following these measures, symptoms typically subside within approximately 30 minutes, although more severe exposures may result in prolonged discomfort, particularly if the incident occurred indoors.
Children are particularly susceptible to these chemical agents due to their smaller physiques and the heightened sensitivity of their pain receptors. “Their tissues are more delicate, their skin is thinner, making it easier for the agent to penetrate their nerve endings,” Jordt states. “Their airways possess a narrower diameter, so any obstruction, swelling, or mucus production presents greater breathing challenges.” Moreover, CS gas tends to accumulate closer to the ground, and children, being shorter, may experience increased exposure, he observes.
Extended Respiratory Complications
The immediate symptoms have been extensively documented. However, the lingering
The consequences of riot control substances are still not well comprehended. Much of what is understood stems from anecdotal evidence, such as accounts from areas of conflict, according to Hassan. Furthermore, numerous investigations have focused solely on healthy individuals, like military conscripts, and do not accurately represent the general populace, as noted by Jordt.
However, even studies involving healthy groups produced concerning outcomes.
A 2014 investigation of over 6,000 army recruits indicated that the likelihood of being diagnosed with an acute respiratory ailment—like bronchitis, sinusitis, and throat discomfort—more than doubled following exposure to tear gas during basic training. In total, 114 recruits received diagnoses for respiratory sickness in the week after exposure to the CS agent, compared to 47 in the week preceding it.
The research also revealed a correlation between higher levels of exposure and an increased probability of illness, and subsequent studies demonstrated that lowering exposure concentrations diminished the risks. This subsequent research indicated that the effects of tear gas lingered for days after exposure in healthy individuals, prompting the military to implement restrictions on exposure levels and durations and enhance decontamination protocols, as stated by Jordt.
These compounds, particularly the CS agent, possess the ability to irritate the sensitive tissues of the eyes and the respiratory passages, causing damage to the lining of the respiratory system and the eyes for a period of time, Jordt explains. This can lead to fluid accumulation in the lungs, resulting in pulmonary edema, which may subsequently lead to infections and other respiratory complications. Following significant or repeated exposure incidents, such damage could potentially result in persistent effects.
The elderly, individuals who smoke, and those with asthma or other respiratory conditions ought to exercise particular caution regarding exposure, says Jordt, as these substances can precipitate or worsen existing respiratory ailments, including infectious diseases. This is a point of concern for residents of Minnesota, as the demonstrations are occurring during the peak season for respiratory viruses, according to Szema.
Additional studies have also drawn connections between respiratory illnesses and exposure to tear gas. For instance, in a 2017 analysis examined by UC Berkeley’s Human Rights Center, Haar and psychologist Jess Ghannam from the University of California, San Francisco, documented the experiences of individuals subjected to tear gas nearly every day in camps within the West Bank. “The long-term consequences were, you know, devastating, such as lung ailments, asthma, difficulties with breathing, and skin sensitivities,” Haar states. While such a degree of daily exposure over extended periods and in densely populated circumstances might be exceptional, it can offer valuable insights into situations like those in Portland, Chicago, and Minnesota, where civilians have been repeatedly exposed to tear gas and pepper spray by law enforcement agencies.
Persistent cardiac issues
While the dangers associated with respiratory problems appear relatively evident, evidence suggests that the effects can extend beyond the immediate respiratory system. In 2025, a cohort of researchers, spearheaded by pediatrician Konstantine Chakhunashvili of Caucasus University in Tbilisi, Georgia, reported a noteworthy incidence of cardiac complications among demonstrators who had been exposed to tear gas during protests concerning the 2024 parliamentary election results in Georgia.
Chakhunashvili and his associates monitored the cardiac function of 69 demonstrators who had been exposed to tear gas at the protests, where canisters containing the CS agent were present. Echocardiogram examinations of the subjects’ hearts—conducted at least five weeks post-exposure—revealed delayed electrical signal conduction in the hearts of approximately one-third of the demonstrators, contrasting with just 7 percent of unexposed individuals. The researchers also identified a marker frequently linked to diminished blood flow in the hearts of around 29 percent of the demonstrators, compared to 3 percent of those who were not exposed.
This indicates a connection between tear gas exposure and “potential issues with blood oxygenation and possible oxygen deprivation of heart muscle” that can persist for weeks, Chakhunashvili states. His team also surveyed over 300 demonstrators, finding that more than a third reported experiencing headaches, ocular problems, skin disorders, elevated blood pressure, or psychological distress extending beyond one month after exposure.
Further investigations are required to establish causality. Nevertheless, “the indiscriminate nature of tear gas should compel at least the democratic nations to implement more stringent regulations on its usage,” he asserts.
Reproductive implications
Researchers in Minneapolis have voiced concerns that tear gas might exert lasting effects on other bodily systems. Hassan resided in southern Minneapolis in 2020 when protests erupted following the death of George Floyd, an unarmed Black man, at the hands of a police officer. “I was hearing… from my neighbors that they were experiencing unexpected changes in their bodies,” she recounts.
Individuals who had not menstruated for years, due to contraceptive use or hormone therapy, reported to Hassan experiencing spontaneous menstrual bleeding in the immediate aftermath of tear gas exposure. “Hearing that just once, I don’t know, might sound like an anomaly,” Hassan remarks. “I heard that multiple times from my neighbors and community members.”
Hassan and her team analyzed survey responses from over 1,200 individuals who had been subjected to chemical agents by law enforcement in 2020 and 2021. In 2023, Hassan and her colleagues published findings indicating that 83 percent of the exposed individuals experienced uterine cramping, breast tenderness, or irregularities in their menstrual cycles (either early or late bleeding). Furthermore, they observed that individuals exposed on more than two occasions were twice as likely to experience an adverse effect compared to those exposed on a single day.
Significantly, 10 out of the 19 individuals who reported being pregnant at the time of exposure indicated a subsequent miscarriage—approximately double the expected rate of miscarriage. While the number of participants is insufficient to definitively link exposure and miscarriage, the finding raises questions about both the short-term and long-term fertility of individuals exposed to crowd control substances, as noted by Hassan and her colleagues in their study.
83
percent
— the proportion of over 1,200 individuals exposed to chemical crowd control agents who reported experiencing uterine cramping, breast tenderness, and menstrual irregularities.
This is not the initial instance of such a correlation being suggested. For example, Haar’s research in the West Bank and a 2012 report detailing the tear-gassing of civilians in Bahrain both documented instances of miscarriages following exposure. Consequently, in 2011, concerns regarding this connection prompted the Chilean government to prohibit the use of tear gas, albeit on a temporary basis.
One hypothesis is that stress plays at least a partial role, according to Jordt. Hassan, however, proposes a more physiological explanation. “It would take a significant amount [of stress] for someone to suddenly experience a spontaneous bleed after years,” she suggests. Another possibility is that these agents interfere with the hormonal systems within our bodies, as both Hassan and Jordt propose, similar to the mechanism by which the plastic compound BPA functions.
Currently, Hassan is gathering data to investigate whether the widespread deployment of tear gas in Minneapolis impacted preterm birth rates in 2020 and 2021, and she may incorporate data from 2025 and 2026 as it becomes accessible. “I repeatedly received correspondence from healthcare providers who had observed an increase in preterm births,” she mentions. “I’m hoping to be able to explore that avenue and gain an understanding of whether there are population-level shifts.”
Research initiatives like Hassan’s are infrequent within the United States, primarily due to a deficiency in federal research funding—a scarcity that predates the Department of Homeland Security’s operational activities in Minnesota. There is essentially no governmental financial support for this type of inquiry, according to Haar and Jordt. “It appears to me that there is no genuine, serious commitment from the government’s side to endeavor to comprehend the health ramifications of these agents,” Jordt concludes.
