The recent social unrest in Hong Kong, brought about by the controversial amendments to the Fugitive Offenders Ordinance (Cap. 503), has put the crowd control actions of the Hong Kong Police Force in the limelight. In 2019, Hong Kong witnessed the most extensive civilian protests since the 1960s, and consequently the police have used crowd control measures to restore social order. 1 In particular, ochlorobenzylidene malononitrile, also known as CS gas or simply tear gas, is deployed during crowd dispersal operations. At the time of writing, over 1800 canisters of CS gas have been used in Hong Kong since June 2019, often in high concentrations in densely populated commercial or residential areas or poorly ventilated areas. This has led to CS gas exposure among not only protestors, but also news reporters, bystanders, and residents and employees in nearby buildings.To better inform local medical practitioners, we present a brief literature review of the clinical effects and risks related to CS gas exposure.