Lead researchers previously found breast milk bought online was highly contaminated with bacteria. Now, an update on that study - it might not even be breast milk at all.
Not only did the investigators find many women selling breast milk on the internet were not offering the real deal, they were also vague about their health.
Of the samples analyzed, four were found to contain Nicotine and Cotinine, compounds which indicates the milk came from a person who has been exposed to cigarette smoke.
Another reason researchers are saying, buyer beware.
Pediatricians say breast milk is healthiest for infants. So to get enough, some mothers are going as far as buying breast milk on the internet.
Researchers at Nationwide Children's Hospital estimate there are more than 55,000 people purchasing or sharing breast milk online.
"It's really hard to know what you are getting," said Dr. Sarah Keim, Nationwide Children's Hospital. "And whether the person on the other end of that email or Facebook conversation is really who you think they are.
"We found that one in 10 samples of milk that we purchased online had high levels of cow's milk or infant formula added to it.
"When people are selling their milk online they may have an incentive financially to top off their milk with cow's milk or baby formula to increase the volume and make more money."
That can be dangerous for moms who are turning to breast milk online because their baby has a dairy allergy.
"They can have a serious allergic reaction or have a lot of gastrointestinal illness when they drink cow's milk," Keim said. "I think it's really buyer beware. You don't know what's in the milk that you are purchasing and I think it's clear from the series of studies we've conducted, that milk purchased on the internet is not safe for babies."
Researchers recommend moms talk to their pediatrician to decide what feeding plan is best.
"Every baby is different and I think it's really important for parents to work closely with their pediatrician to consider the babies health," Keim said.