I’m grateful that all five of my daughters were breast-fed for varying lengths of time (because, every kid is different).

For those who can’t breast feed, for whatever reason, I can see the appeal of buying breast milk from another source, but like any other food, there’s a lot of huckters and buskers out there.

Human breast milk has been sold online for years, and health experts have warned about possible dangers. Now they have a new warning: Some of the milk for sale isn’t strictly human — it’s been topped off with cow’s milk.

That milk could be dangerous for some babies, says Sarah Keim, a researcher at Nationwide Children’s Hospital in Columbus, Ohio.

Keim led a study published Monday in Pediatrics that shows 10 out of 102 breast milk samples purchased online contained at least 10% cow’s milk. The added milk could have come straight from cartons or from baby formula, Keim says.

“It could be very harmful to babies with allergies or intolerance” to cow’s milk, she says.

In a previous study using the same samples, Keim found 75% were contaminated with viruses or bacteria.

The Food and Drug Administration has warned since 2010 that milk sold or shared online could be unsafe.

The samples in the study, purchased in 2012, came from several sites, Keim says, including one called Only The Breast that continues to operate and appears to be the leading site for such transactions. Other sites, such as Eats on Feets and Human Milk 4 Human Babies, facilitate the sharing of milk but discourage sales.