If you’re buying breast milk online (hey, I don’t know what you’re up to) you may have a problem on your hands. A new study shows that more than 10% of breast milk samples purchased online contained significant quantities of cow’s mlik.

According to the New York Times, researchers online shopped for 102 breast milk samples. The sites used “classified advertising” to link up milk buyers and sellers. (A quick Craig’s List search revealed at least one nursing mother in the New York area willing to sell 24 ounces of her own frozen breast milk.) The researchers then tested the mitochondrial DNA of the samples. Thankfully, they all contained some human DNA. Eleven of the samples also contained cow’s milk. Ten of them were made of over 10% cow’s milk.

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The study’s lead author Sarah A. Keim, a principal investigator at Nationwide Children’s Hospital in Columbus, Ohio, says the 10% should be considered more than a minor contamination. “This is deliberate adulteration no matter how you look at it,” she told the Times.

Infants under 12 months shouldn’t be drinking cow’s milk, says Dr. Keim, plus many of the parents who turn to the web for help have babies who can’t tolerate cow’s milk at all. Unfortunately, all they can do is find a more reliable, likely off-line, source.

(For a guaranteed breast milk experience, you can still head to this Chicago spa for a breast milk facial – they collect their samples in person, so there’s that.)

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