Breast milk is packed with nutrients essential for newborn babies. But its health benefits are also driving a shady, unregulated online marketplace—where milk can sell for a couple of bucks per ounce—that is potentially spreading syphilis, hepatitis and even HIV, according to a new study published in BMJ.

Online buyers are usually new mothers looking for organic ways to feed their babies. There’s also the occasional athlete or cancer patient in the forums or posts, seeking out what they consider a natural superfood. However, it’s only a matter of time before a black market milk purchase does real harm to an unsuspecting buyer.

“It’s really, really, really dangerous,” says Sarah Steele, a global health professor at Queen Mary University in London, and co-author on the paper.

More The Black Market for Stolen Baby Formula Is Booming

Prior research suggests that up to 93 percent of unregulated breast milk may be contaminated, Steele says. One disturbing study found dangerous fecal bacteria in three of four unregulated milk samples purchased online, and CMV—a virus that is often harmless in adults, but can cause seizures and death in newborns—in 20 percent of those samples.

Beyond viruses and fecal bacteria, contaminated breast milk can spread sexually transmitted diseases, like HIV and syphilis. Steele also suspects that a few nefarious breast milk dealers go so far as to dilute breast milk, with water or cow’s milk, to increase volume and profits.

Not all donor breast milk is dangerous. Licensed milk banks screen their products for diseases, and pasteurize the milk before shipping it out to mothers. And within closed Facebook groups and websites like OnlyTheBreast.com, roughly 27,000 active members (plus 800 new members every month) trade breast milk—though none of it has been tested.

The best way to protect consumers from disease and deception, Steele says, is by implementing widespread regulation of the breast milk market now—before things get truly out of hand. “There is an urgent need to prevent tampering and contamination,” she says. “We need to address people who are intentionally jeopardizing infants’ health.”