THOUSANDS of mums are sharing their own breast milk via social media in a bid to help those who can't breastfeed, an investigation has revealed.
But the trend is putting babies at risk of infections like hepatitis and HIV that can be carried in breast milk, experts warn.
Advocates argue that mums who buy the milk are making an informed choice.
Bex Poole is one of the mums who used someone else's breast milk to feed her son, Theo.
Theo was no putting on weight at a healthy rate but Bex was reluctant to supplement breast milk with formula.
A friend then suggested she search for alternative options online like the Facebook page Human Milk 4 Human Babies, which facilitates the exchange of breast milk.
"My milk wasn't increasing in any way," she told the BBC.
"I jumped straight on the page, no hesitation, and appealed for help."
But Dr Gemma Holder, a consultant neonatologist at Birmingham Women's Hospital, warned mums who exchange milk could be risking their babies' health.
She works at the hospital's milk bank where milk is donated and vetted in line with the UK's National Institute for Health and Care Excellence (NICE) guidelines. It is one of 16 banks in the UK.
"Fresh donor milk has significant risk of potentially passing on infection, particularly if you don't know how it was handled," she said.
"We know from just screening our milk there are bugs such as E. coli.
"We still get a couple of donors a month, for example, whose milk we aren't able to accept."
Any time a child gets milk from another mum, they are exposed to possible infections, according to paediatrician Dr Wendy Swanson.
Writing for Baby Center she said: "Of course, some argue that sharing breastfeeding duty is an age-old solution for nursing mothers, but nowadays we understand a lot more about the risks of infectious diseases.
"We know that HIV can be transmitted through breast milk, and there is a very small possibility that hepatitis can be passed along if a woman has cracked nipples.
"It might be comforting to think that your sister or a friend could feed your baby if you're not around.
"But unless you know her complete medical history, it would be risky to let another woman breastfeed your baby."