A doctor has issued a warning to parents to keep an eye on their children after a potentially fatal craze has left at least four children needing surgery.
The trend involves placing small magnetic balls inside your mouth to mimic face piercings.
The magnetic balls can cause severe damage to the digestive system if they are swallowed.
Often children will put them in their noses, and even in their eyelids. Some put them inside their mouth and put the corresponding magnet outside it.
The magnets continue to work even inside the body, because the force that draws them together is not disrupted by the thin, porous tissue in the body.
A UK doctor has since written a letter to schools warning of the craze and pleading with parents not to buy magnetic balls for their children.
His letter read: "I would like to highlight the dangers of these highly magnetic balls.
These very small (usually 3-5mm) balls are widely available to buy in the UK and are sold as a "creative toy".
"I cannot emphasise how dangerous these can be if swallowed.
"These balls have already been banned in other countries because of their risk to children.
"You may wonder why a child would swallow these or you may think 'my child wouldn't swallow them' but I plead with you to not take the risk.
"Apparently, some children have been creating a larger ball using numerous small individual balls and putting them in their mouth, they then place other balls on the outside of their face.
"They then use their tongue to move the larger ball in their mouth to make the balls on their face move, which understandably kids find amusing.
"However, some of the individual balls in their mouth can come away and be accidentally swallowed.
"The balls are highly magnetic and when swallowed can cause severe damage to the digestive tract.
"As the balls move through the bowel they can magnetise together even when in different parts of the bowel.
"The pressure applied to the bowel tissue lying between the two magnets is so strong is causes a perforation in the bowel."
In 2019, 6-year-old Libbie Walker needed major surgery and was left with a 7-inch scar after swallowing the magnetic balls.
She suffered a perforated bowel.
In 2018, young boy Freddie Webster also needed part of his bowel removed after a 3mm ball ripped a hole in the wall of his stomach.