One in every ten samples of breast milk bought over the Internet contained significant amounts of cow’s milk, results from a new study showed. Findings from the study, which are published in Pediatrics, are the first to show that milk bought over the Internet is frequently adulterated with intentionally added ingredients.

Human milk that is “topped off” with cow’s milk or infant formula may place babies at risk for infectious diseases from viral or bacterial contamination. Babies with an allergy or intolerance to cow’s milk could also be harmed from drinking the adulterated milk. Earlier research has shown that 21% of people sought human milk online due to a child with a preexisting medical condition, 16% of which were specifically due to their baby’s formula intolerance. In addition, over 75% of milk samples bought online were found to have bacterial or viral contamination.

RELATED: Breastfeeding Benefits, Recommended Duration Updated in Position Paper

Study authors from the Nationwide Children’s Hospital and the Cincinnati Children’s Hospital Medical Center bought and tested 102 samples of breast milk marketed on milk-sharing websites. They compared these samples with their own human milk preparations diluted with cow’s milk to estimate how much was needed to test positive for bovine DNA. The team found that 11 of the purchased samples contained bovine DNA, of which 10 showed results suggesting more than an accidental contamination with cow’s milk. Findings from the study suggest that that sellers intentionally added cow’s milk or infant formula.

Researchers caution that the baby’s safety is not guaranteed when buying breast milk from an unfamiliar source. Pediatricians should counsel patients against obtaining human milk over the internet, and women who have difficulty producing enough milk for their child should work with their pediatrician to find safer ways to feed their baby, they conclude.

For more information visit