CS and OC gases are two widely used chemical agents for riot control causing irritation and discomfort, sharing some common features but distinct chemical compositions and effects. CS gas is an organic compound derived from benzylidenemalononitrile, a member of the lachrymatory agents family, used in the form of an aerosol or as a solid in riot control canisters that release the substance into the air. CS is slightly soluble in water but highly soluble in organic solvents like ethanol or acetone. CS gas primarily works by stimulating the sensory nerves in the eyes, skin, and mucous membranes (especially the respiratory system). When inhaled or contacted, it causes intense irritation of the eyes, nose, throat, and respiratory tract. The symptoms of exposure include eyes intense burning, excessive tearing, blepharospasm and blurred vision, skin redness, irritation, itching, and a burning sensation, coughing, choking, shortness of breath, chest tightness, and potentially wheezing, disorientation, panic, nausea, and headaches. Symptoms usually last 15–30 min, though the discomfort can persist longer, especially if exposure is prolonged. Chronic exposure can lead to lung damage, especially for individuals with pre-existing respiratory conditions. In rare cases, exposure to large quantities or prolonged exposure could lead to permanent damage to the eyes or respiratory system. High concentrations in confined spaces can cause severe respiratory distress and even death, although fatalities are rare.

OC Gas is an oily extract from the fruit of hot chili peppers, particularly from varieties like “Capsicum annuum” and it is usually found in liquid form in pepper spray canisters and can be dispersed as a fine mist, gel, or foam. OC is soluble in oil but not in water and works by irritating the transient receptor potential vanilloid 1, which are responsible for detecting heat and pain. It induces inflammation in the mucous membranes, especially the eyes and airways. Symptoms of exposure include intense burning, watering, swollen eyelids, and temporary blindness, skin severe burning sensation, redness, swelling, and irritation, coughing, choking, difficulty breathing, and a feeling of suffocation, panic, disorientation, and intense discomfort. Some people may experience nausea, dizziness, or vomiting. Burning sensation and discomfort can last from 20 min to an hour, but symptoms can persist longer depending on the amount of exposure.

OC short-term Risks include temporary vision impairment (inability to see for several minutes) and eye pain, respiratory distress, especially for individuals with asthma or other lung diseases, severe discomfort and psychological effects, including panic or anxiety. OC long-term risks include eye damage (prolonged or intense exposure may cause corneal damage or other eye problems), respiratory effects (prolonged exposure or repeated use could exacerbate chronic respiratory conditions like asthma, bronchitis, or emphysema), and skin damage (intense exposure can cause burns or allergic reactions)”.

The immediate or short-term effects of tear gases are usually more noticeable and are due to irritation caused by the chemicals in the gas. They are usually temporary and disappear after moving away from the area of exposure or after rinsing the eyes and face with water. Long-term effects can be more severe and persist after exposure has ended.

People exposed to tear gases may experience symptoms immediately after exposure. The majority are benign with their irritant effects starting within 30 min [21] such as ocular, cutaneous, nasal, digestive and pulmonary [22, 23]. Serious exposures can produce more severe injuries to the eye, skin, and respiratory tract requiring intensive care. But there may also be later effects [24, 25], for example, chest pain can develop at a later moment [26], as well as psychological problems [27].

When exposure occurs in closed places and at high doses of the agent, depending on the dose–response relationship, there may be serious effects such as blindness, glaucoma, and even death due to severe chemical burns to the throat and lungs or due to respiratory failure. Also, nausea, vomiting, and diarrhea have been described if high concentrations are attained, such as when exposure occurs in a confined space or when a long duration of exposure occurs [20].

Long-term effects such as eye problems or respiratory problems [28] and permanent disabling injuries have also been described as a result of the use of these agents in more than 1% of exposed people [29]. Exceptional effects of the type of severe multisystem disease due to hypersensitivity rather than direct tissue toxicity as above have also been described [30].

The frequency of harmful effects depends on the agent, dose used, and conditions of exposure. A systematic review by Haarr et al. In 2017 [31] reported a frequency of 8.7% of serious effects in all body systems that require medical treatment, 17% of moderate effects, and 74.3% of minor effects. CS used to be safe when used at low concentrations (1 part per 100,000,000) as a microparticulate cloud for riot control purposes [32] but experimental studies have found that ocular damage occurs after the application of high concentrations of CS to the eye, especially when applied in solution [33]. There have also been case reports of significant ophthalmological sequelae [34].

This frequency of minor effects coincides with that of our study where the majority of injuries affected the eyes and skin of those exposed with averages of 80% and 74%, respectively. All the effects studied in our study were significantly more frequent in the group of brigade members than in the residents, except high blood pressure, which was more frequent in the latter. This could be due to the different age composition of both groups since the resident group had a significantly higher average age.

The harmful health effects of tear gas have been documented and evidence demonstrates that they have the potential to cause serious harm and present specific threats to vulnerable populations, including children, women, and individuals affected by respiratory, cutaneous, and cardiovascular morbidities [14]

Despite this, the fact that they are generally considered non-lethal and the limited duration of most of the effects, most of them lasting less than two weeks except in some cases with previous pathologies such as asthma [35], may lead one to think that they are relatively harmless, which is not true [36–39]. Therefore, more research is needed to elucidate which conditions of use should be avoided and a serious reevaluation of chemical safety and more comprehensive exposure follow-up studies are necessary [15, 40]. From the toxicological point of view, we need more epidemiological and laboratory research to know the health consequences of exposure to full tear gas compounds such as CS. The possibility of health consequences in the long term, such as cancer, reproductive effects, and lung disease is particularly worrying given the multiple exposures suffered by demonstrators and non-demonstrators too in some areas of civil unrest [41–44].

This study has several limitations: the first one is that the harmful effects collected were “self-perceived” by the participants and not diagnosed by a medical professional. The second one is that obtaining an adequate sample in emergency situations with violence is difficult because the participating population in consecutive riots was not stable, unknown and numbers changed every day. It is also not possible to obtain a census of participants from which to obtain a representative sample. So, the sample only collects the information from the people who answered the questionnaire. The third one is that in the context in which the study was conducted (a riot area with high violence and a population that is very mobile from one area to another) it was impossible to analyse whether each participant was in an area with a certain concentration of tear gas dispersion.

As a conclusion, Chlorobenzylidenemalononitrile and Oleoresin Capsicumtear gas during social unrest in the Plaza de Italia area of Santiago, Chile between October 2019 and March 2020 produced health harmful effects on both the residents of the area and the brigade volunteers who provided health care for those affected. More than half of the exposed people studied presented eye pain or burning, throat irritation, respiratory difficulty, skin pain or burning, and impaired vision. And more than one in three had skin erythema, headache, and irregular breathing. Twenty two of the negative effects were significantly more frequent in the group of brigade members than among the residents and only high blood pressure was significantly more frequent among the residents.

In the first hour after exposure (immediate effects), the most frequent effects were pain or burning, impaired vision, respiratory difficulty, irregular breathing, skin pain and burning, skin erythema, nausea, tachycardia, and hypertension, all of which were significantly more frequent among the brigade members than among the residents. Between one hour after exposure and 24 h later, the most frequent effects were diarrhea, skin vesicles, and eye pain or burning, all of which were significantly more frequent among brigade members than among residents. Between 24 h and several days after exposure, the most frequent effects among brigade members were conjunctivitis, skin pain, burning, rhinitis, and diarrhea. Among residents, they were skin pain, burning, and impaired vision.