Some children's slime toys contain potentially unsafe levels of a chemical which can cause vomiting and impair fertility, according to Which?.
An investigation by the consumer group into 11 popular slime products found eight contained higher than recommended levels of a chemical called boron.
One product had more than four times the EU safety limit, the tests found.
Which? is advising parents to "approach slime with caution" and said retailers and the government must do more.