DENVER -- Mothers looking to buy or sell breast milk are now turning to the Internet as an alternative and that's causing some concerns for a local milk bank.

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Some mothers believe they can do their own screening process since it's more expensive to buy through a milk bank, but others say private screening is still not enough.

Becky McGraw said when she began pumping, she found that she had quite a bit of extra milk, so she decided to become a donor for HealthONE Alliance Mother's Milk Bank, located at Presbyterian St. Luke's Medical Center in Denver.

She said that at first, she thought about selling it over the Internet.

"At one time, it crossed my mind that if that baby gets sick, they might think it's something wrong with me or my milk," McGraw said.

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Liability is one of many reasons why Mother's Milk Bank is urging people not to buy or sell breast milk through the Web.

"Sharing milk informally is a dangerous thing to do," said Laraine Borman, director of the Mother's Milk Bank. "Diseases such as HIV and hepatitis can be transmitted through human milk."

At Mother's Milk Bank, one of the largest of only seven banks in the country, donors go through a thorough screening process, including blood tests and pasteurizing the breast milk. It's more costly than buying the milk online -- the average can be about $30 a day per baby -- but some mothers say there's no price for that piece of mind.

The practice of women sharing breast milk is nothing really new. It's been going on for centuries -- dating back to the era of wet nurses. What is new is a phenomenon in which women, often perfect strangers, exchange breast milk through the Internet, in mommy chatrooms, and even through mainstream sites like Craig's List and eBay.

Recent student have shown that breast milk reduces a baby's risk of infection, sudden infant death syndrome, and even of childhood cancers.

That's why when Jenn Connel, who had undergone a double mastectomy, had learned that she was pregnant, she was worried she wouldn't be able to feed her first child.

She said she couldn't afford the cost of milk from the bank, so she created her own site -- FeedmyBaby.com. She asked for donations and connected with several women who were able to share their breast milk. She said that until insurance companies start covering the processing fees of milk banks, she thinks this is just as economical and often just as safe.

Connel said she went to extreme measures to screen the women who donated breast milk to her. She worked with her doctor to screen the donors, to prepare questionnaires, to even have the women submit results of blood tests their own doctors conducted -- all to insure that the women who were donating breast milk were helping, not hurting, her baby.

But the practice of donating breast milk through the Internet remains controversial.

"There's no screening on the Internet," McGraw said. "Someone else could carry infections, that baby would be at risk otherwise."