Results from a recent study led by Nationwide Children’s Hospital researchers has found that over three-fourths of breast milk samples purchased online contained bacteria that could cause illness in infants. It was also discovered that the samples frequently exhibited signs of poor collection, storage or shipping practices.

This study is the first ever to examine how safe the online selling of breast milk to others is. The trend has become a fairly frequent practice in the past several years. It is unknown exactly how common purchasing breast milk online is, but a previous study found that 13,000 postings were placed on U.S. milk sharing websites in 2011 alone.

The research team behind the study purchased their breast milk samples from listings on various public websites and then analyzed each one in a lab. The research was completed in collaboration with Cincinnati Children’s Hospital Medical Center and The Ohio State University.

“We were surprised so many samples had such high bacterial counts and even fecal contamination in the milk, most likely from poor hand hygiene. We were also surprised a few samples contained salmonella,” said Sarah A. Keim, PhD, principal investigator in the Center for Biobehavioral Health. “Other harmful bacteria may have come from the use of either unclean containers or unsanitary breast milk pump parts.”

The researchers only responded to for sale ads that did not ask about the infant receiving milk and did not require a phone call before a transaction would be made. They analyzed 101 different samples that were purchased online and compared their findings to 20 samples obtained from a milk bank.

Shipping practices appeared to play a major role in the levels of bacteria in the milk purchased online. The longer the shipping time, the more contaminated the milk. Nineteen percent of sellers that were purchased from did not even include dry ice or another cooling method so the temperature of the milk was outside of the recommended range for storage. Researchers found high levels of one or more types of bacteria in 17 percent of all the samples.

“Major milk-sharing websites post a lot of guidance about milk collection, storage, shipping and provider screening. However, results from this study showed sellers do not often follow this advice because hygiene and shipping practices were often compromised,” said Dr. Keim, a faculty member at The Ohio State University College of Medicine. “Based on our research, it is not safe to buy breast milk online, and the Food and Drug Administration recommends against sharing milk obtained in that way. Recipients are not able to determine for sure if the milk has been tampered with, or contains harmful drugs or pharmaceuticals, or if the information the provider supplied about their health was truthful.”

This study was published in the November issue of Pediatrics.