Georgia's authorities used a World War One-era chemical weapon to quell anti-government protesters last year, evidence gathered by the BBC suggests.
“You could feel [the water] burning,” one of the protesters said of water cannon turned on him and others on the streets of the capital Tbilisi. A sensation, he said, which could not immediately be washed off.
Demonstrators against the Georgian government's suspension of its European Union accession bid have complained of other symptoms too - shortness of breath, coughing, and vomiting that lasted for weeks.
The BBC World Service has spoken to chemical weapons experts, whistleblowers from Georgia's riot police, and doctors, and found the evidence points to the use of an agent that the French military named camite.
The Georgian authorities said our investigation findings were absurd and the police had acted legally in response to the illegal actions of brutal criminals.
Camite was deployed by France against Germany during World War One. There is little documentation of its subsequent use, but it is believed to have been taken out of circulation at some point in the 1930s, because of concerns about its long-lasting effects. CS gas - often referred to as tear gas - was used as a replacement.
Konstantine Chakhunashvili was one of those who gathered outside Georgia's parliament in Tbilisi during the first week of protests - which began on 28 November 2024. Demonstrators were incensed by the ruling party's announcement that it was pausing EU accession talks. The goal of EU membership is enshrined in Georgia's constitution.
Georgia's police responded with a variety of riot-control measures including the use of water cannon, pepper spray and CS gas.
Dr Chakhunashvili, a pediatrician who was among those sprayed by the cannons, and who has taken part in many of the demonstrations, said his skin felt like it was burning for days, and the sensation couldn't be washed away. In fact, he said, it was worse when trying to wash it off.
Dr Chakhunashvili wanted to find out if others had suffered similar effects. So he appealed, via social media, for those also targeted by crowd control measures during the first week of the demonstrations to fill out a survey. Nearly 350 people got in touch, and almost half said they had suffered one or more side effects for more than 30 days.
These long-term symptoms ranged from headaches, to fatigue, coughs, shortness of breath and vomiting.
His study has been peer-reviewed and has been accepted for publication by Toxicology Reports, an international journal.
Sixty-nine of those surveyed by Dr Chakhunashvili were also examined by him and found to have significantly higher prevalence of abnormalities in the electrical signals in the heart.
The effects of that product, he says, were unlike anything he had previously experienced. He found it difficult to breathe after standing close to where it had been sprayed, and he and the 15-20 colleagues who tested it with him could not easily wash it off.
Speaking from his new home in Ukraine, he tells the BBC that when watching footage of the protests last year, he immediately suspected that demonstrators were being subjected to the same chemical.
The BBC spoke to another former high-level police officer who confirmed that whatever was loaded into the water cannon vehicles was the same compound deployed in the protests of November-December 2024.
Experts have pointed out that the use of such a chemical could classify as a chemical weapon, given its severe and persistent effects on the population, which violates human rights law.
The protests on Tbilisi's Rustaveli Avenue have dwindled in size but not in frequency, remaining a call for the resignation of a government accused of rigging elections and siding with Russian interests.
The ruling Georgian Dream party denied these accusations and affirmed that their legislative changes served the best interests of public welfare.
