Doctors have issued a warning over tiny beads that can expand up to 400 times their original size when exposed to liquid, amid reports linking them to serious harm and deaths among children.
The water beads are marketed for various purposes, including for use as toys, in crafting, as home decor or in floristry, and are especially popular at Christmas. They are sold under a variety of names including jelly balls, water balls, sensory beads and water crystals.
If swallowed, water beads expand and can block the gastrointestinal passage, which may then require surgery. The beads can also cause choking and have harmed children in the UK, with reports linking them to deaths globally. Water beads can be difficult to detect and do not show up in X-rays.
On Monday, the Royal College of Emergency Medicine (RCEM) issued a "safety flash" over water beads marketed as toys, amid fears they could be given to young children over the holiday period.
It follows a safety alert from the UK's Office for Product Safety and Standards, which advised that water beads should be kept away from children under five years old, and only used with older children or vulnerable adults under close supervision.
Water beads have been linked to child deaths overseas and to "serious harm" to children in the UK, the RCEM said. They are sometimes used in stress balls and sensory toys, and they are also sold as home decor and vase fillers.
The beads start small, only a few millimetres wide, but can grow to 400 times their size in about 36 hours when exposed to liquid.
The safety alert has been issued to emergency doctors to ensure they know what to look out for while working, but the RCEM also wants to warn parents and carers of the dangers.
The RCEM's alert also highlighted concerns about the potential for children to swallow button or coin batteries and magnets, which pose a danger to children and vulnerable adults if swallowed.
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The RCEM vice-president Dr Salwa Malik said: "Any one of these three objects could be found under your tree or in a stocking this festive season, hidden in gifts that are intended to bring joy to a child or vulnerable person, but which, if swallowed, could result in critical illness and the need for emergency medical treatment.
"As an emergency medicine doctor, I have seen parents holding their child's hand and watching over them while they lay on a bed in an emergency department, in need of urgent care because they have ingested one of these items.
"As a parent, I can imagine how utterly terrifying and traumatic that would be to go through - for a mum, dad, grandma, grandpa, aunt, uncle, brother, sister and, of course, the child themselves.
"Having seen the effects first-hand, which can be devastating and detrimental, we are asking people to please think twice about the dangers these pose while selecting and gifting presents this season."