The online ads are straightforward and sincere: Healthy mother looking to sell extra breast milk. Two dollars an ounce.

You can find them all over the Web, from Craigslist to online message boards to onlythebreast.com, a site devoted to the buying and selling of breast milk. And, despite numerous warnings from health experts, people are purchasing breast milk over the Internet to feed to their babies.

The practice is extremely dangerous. Accepting milk from an unregulated source – whether it’s the Internet or a well-meaning friend – exposes your baby’s vulnerable immune system to a host of diseases. Breast milk, like other bodily fluids, can transmit HIV, hepatitis and other viruses. There’s also no way to know how long the milk has been stored or whether it has been contaminated.

So why do people do it? Well, many studies tout the benefits of breast milk. It’s reported to help protect babies from disease, boost their immune systems and lower the risk of obesity. Yet not every mother is able to breastfeed, perhaps due to medical reasons or maybe because of adoption.

The Internet is not the only option for buying breast milk but it is the cheapest. Milk typically sells for around one or two dollars an ounce online, versus four or five dollars an ounce at one of the country’s eleven certified human milk banks.

As of now, only California and New York have restrictions on the sale of breast milk. It’s still legal in most other states. But that doesn’t make it wise. For those who are serious about procuring it, it’s best to turn to milk banks, which are typically found in hospitals and are regulated by the Food and Drug Administration. They screen the fluid and ensure it is safe as, well, mother’s milk.