Buying breast milk is tempting to new parents struggling to express their own, as it provides babies with better protection against illnesses and allergies compared to formula.
"Our discrete breastfeeding breast milk classified system makes it possible to sell or buy breast milk in a clean, private way," a website was quoted by the Daily Mail as saying.
Donor mothers list their milk under the age of their baby and if they can provide fresh milk on demand.
A search around the site revealed that women from Essex to Newcastle are offering it either fresh or frozen for around 1 pound per fluid ounce, while USD 2 per ounce is the standard rate in the US.
There are legitimate ways to both donate and receive breast milk for free via milk banks. These centres store breast milk for babies whose mothers can't breastfeed.
The banks collect expressed milk from pre-screened mothers who have a plentiful supply and a baby under six-months old. It is then pasteurised before it is offered to nearby hospitals.
But doctors in Germany have warned new parents against privately obtaining their baby's food through social networks such as Facebook.
The Professional Association of Pediatricians said that although breast is generally the best option for newborns, mothers unable to breastfeed should not turn to the internet.
"Donors can be taking medicines or drugs, have infectious illnesses like AIDS or Hepatitis," Wolfram Hartmann, president of the association, said.
"Nobody can check whether the unknown mother's milk is harmless for the particular child," he warned, adding that the milk's quality could also be affected during its transportation.
The warning follows a report by the online edition of German news weekly Der Spiegel and the association's own research, it said.
It also warned that a newborn's nutritional needs differed from those of a baby even of several weeks or months old.
"The milk of a woman who already has an older child does not contain the right nutrient composition for a newborn," it added, and said women who were unable to breastfeed should use special powdered milk.
