A group of parents are calling on the government to release details of the chemical composition of the tear gas being used by police, saying in just four days, they have collected around 1,200 complaints regarding children being affected by the gas.

The Hong Kong Mothers group said it collected online responses from 1,188 people between November 22 and 25 and the complaints received included skin allergies, coughing and dry throats.

It said from the details they got, the youngest victim was just two months old.

It said the complaints came from across Hong Kong, with Yau Tsim Mong district topping the list with Tsueng Kwan O and Island East in the next two spots.

A mother named Sammy who attended the press briefing, said her daughter has eczema and studies in a Kowloon Tong school. She said that after police fired tear gas in the area, the skin condition started to get worse.

The skin became redder and she had to call in sick and see a doctor, the mother said.

A social worker named Cheung said his eight-year-old son who has a skin allergy now has to carry a gas mask with him when he goes out, as the area they live in, Sheung Shui, was heavily tear gassed two weeks ago.

"It is ridiculous that an eight-year-old boy has to carry a gas mask with him, not toys," said Cheung.

Kenneth Kwong, who is a well respected teacher with a doctorate in chemistry from Hong Kong University, said the intense use of tear gas will spread its effects beyond the intended area.

He said the main component in tear gas, called CS, should only be active within an area of 50 metres. But if a large number of canisters are used, it’s possible the effect would be felt across a wider area.

Kwong said he knows someone living in Ma On Shan who felt the effect of tear gas fired during clashes at the Chinese University.

He said tear gas is not exactly smoke that fades, but solid particles which stick to surroundings. So people shouldn’t use water jets to clean up affected places as this will only make residue particles “jump up” from the ground and cause more harm. Instead the surfaces should be cleaned with wet towels, to wipe the particles away.

Sealing Cheng of the Mothers Group said the authorities have to tell the public what chemicals are contained in the tear gas and evaluate the health effects.