Human breast milk sold online to adult buyers "poses many risks" including diseases such as HIV, hepatitis B and C and syphilis, experts have warned.
Often bought by mothers who are unable to breastfeed, b reast milk sold online can be cheaper than that from regulated milk banks and has emerged as a "recent craze" for cancer sufferers, fetishists and bodybuilders.
But an academic at Queen Mary University of London (QMU) warned that the purported benefits of breast milk, hailed as a "super-food" by those who use it, did not meet clinical standards.
Writing in the Journal of the Royal Society of Medicine, Dr Sarah Steele said: "Online forums are replete with posts boasting about the immune, recovery, nutritional and muscle building benefits of human milk.
"Such purported benefits do not stand up clinically, however. Nutritionally, there is less protein in breast milk than other milks like cow's milk. Chemical and environmental contaminants are known to make their way into breast milk, just like the food chain more broadly."
Bacteria was detected in 93% of samples, according to research cited by Dr Steele.
This was due to a lack of sanitisation, pasteurisation and testing and meant the milk could contain contaminants such as alcohol, chemicals and other milk products used to bolster the volume for profit, she said.
Dr Steele added breast milk also contained less protein than cow's milk and should not be taken in place of a balanced diet.
"In sum, breast milk purchased online is not optimal for adult nutrition or in the treatment of disease, as milk bought online poses more risks than proven benefits," Dr Steele wrote.
"Health professionals and regulators both must be aware of this growing trend and issue public guidance against the purchasing of human milk from Internet sources for adult as well as infant feeding."
Experts at the Global Health, Policy and Innovation Unit at QMU have previously warned buying human breast milk on the internet poses serious health risks to babies and called for tighter regulation of the market.