Boron is found in the compound borax, which is used to make slime thick and sticky. Picture: Wikimedia Commons

London - Sticky, gloopy and with something of an ick factor, it’s the playground fad that has entertained children for decades.

But brightly-coloured "slime" may be harmful to their health.

Consumer watchdog Which? has found some slime products contain potentially unsafe levels of the chemical boron, which in excessive levels causes short-term bouts of diarrhoea, vomiting and cramps.

Boron is found in the compound borax, which is used to make slime thick and sticky.

However the European Chemicals Agency warns boron may damage fertility and cause serious eye irritation – and could cause harm to unborn children if pregnant women come into contact with it. 

Nikki Stopford, director of research and publishing at Which?, said: "Parents buying slime for their children... will be shocked to find that the health of their children could be put at risk."

Home-made slimes have previously raised concerns over borax, with reports that children have suffered injuries after trying to copy slime recipes found online. But Which? is now calling for "fundamental changes" to the product safety system after its tests.

Daily Mail