If you've got a child of a certain age, there's a pretty high chance they're into slime – either making it themselves at home or from a shop-bought DIY kit or simply badgering you to shell out for the ready-made stuff.


So, what should you make of all the headlines about tests carried out by the consumer group Which? that claim a number of ready-made slimes contain higher levels of the chemical boron than is allowed under EU safety standards?

Are high boron levels in slime really dangerous for my child?

Boron is found in borax (or boric acid), which is the 'activating' ingredient that gives slime its slimy consistency.

Over-exposure to boron can cause skin irritation, vomiting, cramps and diarrhoea. At very high levels of exposure, it is thought that it may also affect fertility or cause harm to unborn children in pregnant women.

Below, you can find the details on the slimes that Which? found to fail EU safety levels BUT first we want to share what an expert on borates told us about boron, so you can decide for yourself how risky it really might be to let your child play with slime containing borax – both at levels exceeding the EU safety test and at a 'safe' level.

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David Schubert PhD, is a chemist from the USA who has worked with borates and is a recognised expert on the chemistry and applications of borax, boric acid and other borates.

He told us that he is not a toxicologist or an expert on chemical regulatory matters, especially in Europe, but he does have opinions on the EU regulations about borates, saying:

'In my opinion, the EU has taken an unreasonable and even irrational regulatory stance towards borates, citing data for animal studies involving chronic exposure levels that are not realistic for any normal handling and use scenarios.

'I believe borax and borax-containing slime is safe to handle.

'Nevertheless, I am not a regulatory authority and do not want to be seen as enticing anyone to violate any local regulations. I might disagree with a law, but it’s still a law."

David goes on to explain that:

  • People have been handling borate for many years without harm. 'Handling and coming into contact with borax, borax-containing slime, boric acid-containing contact lens solutions, eye drops etc is not hazardous. People have been doing this without harm for many decades.'
  • Borates are not unsafe to handle. 'Borates are toxic and should not be used as intentional food additives, but this does not mean they are unsafe to handle. Many common consumer and personal-care products are toxic to some extent but we don’t eat them.'
  • Borax would only be dangerous if you consumed it on a daily basis. 'Borates have low acute toxicity. If you were to consume the amount of borax present in a handful of slime they might, at most, become sick to your stomach and vomit, but no other harm would result from such a one-off exposure. Only if you were to consume that amount of borax on a daily basis could you suffer any ill effects.'
  • Borates are NOT absorbed through healthy skin. "Borates are not absorbed through intact skin.You can find scientific articles supporting this, such as Wester, et al, Toxicological Sciences, 1998, 45, 42-51.'
  • There is no evidence that borates in humans causes birth defects. 'Although animal studies involving chronic exposure to high levels of borates have shown specific birth defects, which is [a] source of the current hysteria, I am not aware of a single documented human birth defect linked to borate exposure. Nevertheless, it is prudent to regulate borates and not allow them to be used as intentional food additives.'
  • Boron is actually part of a healthy diet. 'Because all plants require and contain boron, boron is a part of a normal healthy human diet. The average person in the UK consumes 1-2 mg of boron daily as part of a healthy diet, which is equivalent to 2-4 mg of borax, and probably more if they are vegetarian or eat a lot of things like nuts and avocados (a naturally very high borate content food).'

In a nutshell, says David: 'Workers in the borate industry work around and come into contact with gigantic piles of thousands of borates every day for their entire careers. If you read the epidemiological studies of these workers showing no adverse health effects, including no reproductive effects, it's pretty silly to think that handling a handful of slime one afternoon will do anyone any harm.'

Which slimes failed the Which? tests?

Which? conducted 2 rounds of tests on slime products. The first was in July 2018 and you can see the product that failed their test in the illustrated table below.

Results of the second round of tests are published in December 2018 and the following products were added to the list of products that failed...

  • Frootiputti, produced by Keycraft and for sale in Hamleys. Keycraft has refuted the Which? findings, pointing out that their product is a putty and its boron levels are well within EU safety limits for putties. Hamleys says it's now removed Frootiputti from its shelves.
  • HGL's Ghostbusters Slime, sold in Smyths Toys Superstores. HGL has also refuted the Which? findings, releasing its own test results and insisting their product is a putty and nothing it contains exceeds safety standards.
  • Fun Foam, made by Zuru Oosh and sold by Argos
  • The DIY Slime Kit, made by Essenson and available from Amazon
  • Jexybox 30z Glossy Slime in pink, sold by eBay
  • ME Life TicTock Fluffy Slime in pink, sold by Amazon.

We want to say right here, too, that MadeForMums has contacted representatives for all of the slime kits featured in our 8 of the best slime making kits article to find out what the levels of boron used are for each one.

We'll add in the results as soon as we have them.

What's the EU safety level for boron in children's toys?

The permitted level of boron in children's toys is 300mg/kg.

The worst offender of the first batch of slimes tested by Which? was Jupiter Juice by Toysmith, sold on Amazon, which was shown to contain 1,400mg/kg.

Here's a list of the slimes that failed the first Which? tests...

The worst 5 (published by Which? in July 2018):


These also failed safety tests:


Which ones passed the July Which? tests?

Three slime products passed the Which?tests:


The Which? report also cites studies that have shown high levels of boron in animals can affect birth weight, birth defects and developmental delays.

It should be pointed out that this was an animal study, however, not tested out on humans. But if you are at all worried you might want to refrain from using slime with an older child if you are pregnant.

The bottom line

If you're thinking of buying slime, you may want to make sure a) you get it from a trusted retailer and b) that it has the CE mark on it which means it conforms with European safety guidelines.

If you've already bought some from the list of those that failed safety tests here, you may want to bin it and invest in a new tub.

But, according to our expert, unless your child is EATING the stuff pretty much every day, it's extremely unlikely that slime toys containing borax will do damage to your child's health.

Top image: Getty / Slime results tables: Which?

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Tara BreathnachContent Editor and Social Media Producer

Tara is mum to 1 daughter, Bodhi Rae, and has worked as Content Editor and Social Media Producer at MadeForMums since 2015