Purchased samples of human breast milk online may be "topped off" with cow's milk or infant formula, according to a recent study.

Researchers from The Ohio State University and Cincinnati Children's Hospital Medical Center found that 10 percent of human breast milk samples bought over the internet contained added cow's milk. The discovery that purchased samples of human milk may be purposely topped off with cow's milk confirms a danger for the large number of babies receiving the purchased milk due to medical conditions. These babies are also vulnerable to the risk of infectious disease from bacterial and viral contamination of such milk.

"We found that one in every 10 samples of breast milk purchased over the Internet had significant amounts of cow's milk added, and this poses a risk to infants with an allergy or intolerance to cow's milk," Sarah A. Keim, lead author on the study, said in a statement. "If a baby with cow's milk allergy were to drink this milk, it could be very harmful."

The team's previous research found that 21 percent of individuals seeking human milk online did so for a child with a pre-existing medical condition. And 16 percent of these parents specifically sought out the purchased human milk due to their baby's formula intolerance.

Also troubling is their prior discovery of bacterial or viral contamination in more than 75 percent of milk samples purchased online, which became the first data to confirm the Food and Drug Administration's 2010 warning of possible contaminants in unpasteurized human milk obtained from sources other than the baby's mother.

The recent study is the first to document that milk purchased online is frequently adulterated with intentionally added ingredients.

For the study, researchers purchased and tested 102 samples of breast milk advertised on milk-sharing websites. They then compared the purchased samples with their own preparations of human milk diluted with cow's milk to approximate the amount of contamination required in order to test positive for bovine DNA.

The findings are detailed in the journal Pediatrics.