Toy slime has been a childhood favorite for decades, and nowadays many people hop on Pinterest and other websites to find recipes for slime that they can make with their kids. But many of the popular slime toys marketed to kids – as well as DIY recipes – contain unsafe levels of boron, a chemical linked to vomiting and fertility problems, according to a consumer advocacy group. 
Being exposed to high levels of boron can cause skin irritation, diarrhea, vomiting, and stomach cramps. At very high levels, the substance can impair fertility and harm fetuses in pregnant women.
A public warning about boron-containing slime was necessary, as most slime products contain very little information about the ingredients contained within them, or what the risks of being exposed to those ingredients are. Some of the toys do carry a CE safety mark but still contain excessive boron.
Which? warned that parents should also be cautious about homemade slime, which often contain ingredients such as contact lens solution and boron, yet many recipes don’t list exact amounts.
A spokesperson for Which? said:
“While we are not outright declaring all slime as unsafe, the warning signs are there from our testing. Certainly, if anyone has bought one of the slimes that has failed, they should return it straight away. But concerns about borax in toys have been circulating. The Italian consumer group recently flagged safety concerns with borax levels in slime given away with newspapers or magazines.”
So far, there have been no reports of illnesses or injuries caused by toy slime.
How the Toy Slimes Tested
Per European Union (EU) safety recommendations regarding liquid or sticky toys, a product should contain no more than 300mg/kg of boron. 
Of the 11 slime toys tested, Toysmith Jupiter Juice was found to be the worst, containing 1,400mg/kg of boron.
CCINEE Pink Fluffy Slime came in 2nd, at 1,000mg/kg, followed by Cosoro Dodolu Crystal Slime Magic Clay, which contained 980mg/kg of boron.
The maker of Mini Bucket Putty, Baker Ross, states that the toy contains safe levels of boron because it should officially be called a putty, not a slime. But Which? disagrees, saying that both the texture and substance of the product makes it a slime. Baker Ross has since taken Mini Bucket Putty off the market, pending further investigation.
Here’s how the other tested products stacked up:
- iBase Toy’s Slime Toy – 860mg/kg
- LOYO’s Fluffy Slime – 730mg/kg
- Brezeh’s Free Slime Toy and Virtuotrade’s My Fluffy Slime – 560mg/kg
The following slime toys fell within the safe limits:
- HGI Goopy Slime
- Glam Goo Deluxe Pack
- Planet Slime Shop’s Hulk Green Halloween Slime
All of the slime toys tested by Which? were available for purchase on Amazon. However, in light of the test results, the retailer has removed them from their U.K. site. Many of the products are still available on the U.S. site. 
In a statement, Amazon said:
“All Marketplace sellers must follow our selling guidelines and those who don’t will be subject to action, including potential removal of their account. The products in question are no longer available.”
But the bad news doesn’t have to mean an end to sticky, slimy fun for kids. A quick Internet search for “natural slime recipes” yields countless recipes that contain safe ingredients that won’t potentially hurt children, adults, or developing fetuses. Or you can choose one that ranked ‘better’ on the list.