The Consumer Council on Thursday warned of health risks arising from shoes for primary school students after finding harmful substances in nearly half of samples that it tested.

It urged manufacturers to improve the designs and materials used to make the shoes to protect children’s health.

Kenneth Chan, the vice chairman of the watchdog’s committee on sustainability, public affairs and education, said the council purchased 28 pairs of different student shoe models from retail outlets at prices ranging from HK$198 to HK$599.

Chemical tests showed that 13 pairs of shoes contained harmful substances, including chromium VI, which can cause lung cancer, and reproductive toxicant plasticisers.

“Using leather containing chromium VI could cause rashes, ulcers and allergic reactions resulting in contact dermatitis,” Chan said.

“Two models were detected with 4.5mg/kg and 5.0mg/kg of chromium VI in their lining, both exceeding the EU limit.

"Although children generally wear socks with shoes, the risk of contact with chromium VI in shoes cannot be completely ruled out.”

The plasticisers, which affect human hormone levels, were detected in four samples, with the concentration in one sample exceeding the European Union limit by nearly 86 times.

“Generally, plasticisers are not readily absorbed by human skin, but with wounds or eczema the risk of absorption increases,” he said.

“Parents should also teach their children to wash hands after putting on or taking off their shoes to avoid indirect ingestion of plasticisers through contact with the mouth or food.”

Chan said two shoe models also showed cracks after 35,000 or 50,000 flexes in durability tests.

Children should try on shoes in person and avoid wearing those that are bigger by one size, he added.