Women's accessories sold by some of the world's most popular online shopping firms contained toxic substances sometimes hundreds of times above acceptable levels, authorities in Seoul said Wednesday.

Chinese giants including Shein, Temu and AliExpress have skyrocketed in global popularity in recent years, offering a vast selection of trendy clothes and accessories at stunningly low prices that has helped them take on US titan Amazon.

The explosive growth has led to increased scrutiny of their business practices and safety standards, including in the European Union and South Korea, where Seoul officials have been conducting weekly inspections of items sold by online platforms.

In the most recent inspection, 144 products from Shein, AliExpress and Temu were tested, and multiple products from all companies failed to meet legal standards.

Shoes from Shein were found to contain significantly high levels of phthalates—chemicals used to make plastics more flexible—with one pair 229 times above the legal limit.

"Phthalate-based plasticizers affect reproductive functions such as sperm count reduction, and can cause infertility and even premature birth," an official from Seoul's environmental health team told AFP.

One such chemical "is classified as a human carcinogen by the International Cancer Institute, so special care should be taken to avoid long-term contact with the human body", they added.

Formaldehyde, a chemical commonly used in home building products, was detected in Shein's caps at double the allowable threshold.

Two bottles of nail polish from Shein were found to have dioxane—a possible human carcinogen that can cause liver poisoning—at levels more than 3.6 times the allowed limit and methanol concentrations 1.4 times above the acceptable level.

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Seoul authorities found sandals from Temu contained lead in the insoles at levels more than 11 times the permissible limit ...