As with all non-lethal or less-lethal weapons, there is a risk of serious permanent injury or death when tear gas is used. This includes risks from being hit by tear gas cartridges that may cause severe bruising, loss of eyesight, or skull fracture, resulting in immediate death. A case of serious vascular injury from tear gas shells has also been reported from Iran, with high rates of associated nerve injury (44%) and amputation (17%), as well as instances of head injuries in young people. Novel findings suggest that menstrual changes are one of the most commonly reported health issues in women.
While the medical consequences of the gases themselves are typically limited to minor skin inflammation, delayed complications are also possible. People with pre-existing respiratory conditions such as asthma are particularly at risk. They are likely to need medical attention and may sometimes require hospitalization or even ventilation support. Skin exposure to CS may cause chemical burns or induce allergic contact dermatitis. When people are hit at close range or are severely exposed, eye injuries involving scarring of the cornea can lead to a permanent loss in visual acuity. Frequent or high levels of exposure carry increased risks of respiratory illness.
Venezuelan chemist Mónica Kräuter studied thousands of tear gas canisters fired by Venezuelan authorities since 2014. She concluded that the majority of canisters used the main component CS gas, but that 72% of the tear gas used was expired. She noted that expired tear gas "breaks down into cyanide oxide, phosgenes and nitrogens that are extremely dangerous".
In the 2019–20 Chilean protests various people have had complete and permanent loss of vision in one or both eyes as result of the impact of tear gas grenades.
The majority (2116; 93.8%) of protestors who reported exposure to tear gas during the 2020 protests in Portland, Oregon (USA) reported physical (2114; 93.7%) or psychological (1635; 72.4%) health issues experienced immediately after (2105; 93.3%) or days following (1944; 86.1%) the exposure. The majority (1233; 54.6%) of respondents who reported exposure to tear gas during the 2020 protests in Portland, Oregon (USA) have also reported receiving or planning to seek medical or mental healthcare for their tear gas-related health issues. It has been shown that health issues associated with the exposure to tear gas are often require medical attention.