Samantha Underwood drove from her home in Waynesboro to a rest stop outside Troutville every two weeks last summer.

She always made the 75-mile trip with a cooler. The cooler was critical. Its contents could change lives, and the precious cargo needed protection from the unrelenting summer heat. Underwood once bought an $800 power generator to ensure it wouldn't spoil in her deep freezer during a power outage.

In that small parking lot off I-81, Underwood gave another mom a two-week supply of her own breastmilk. She never accepted any payment, though she could've sold the liquid online for several dollars an ounce. This was her way of giving back.

Underwood knew firsthand what it's like for a woman to struggle to feed her own baby. Trying to breastfeed her first child, now almost 4 years old, left her exhausted and discouraged.

When several months of effort and frequent visits to a lactation consultant yielded little progress, Underwood was reluctant to switch to formula. She said she wanted her baby to benefit from the nutrients and antibodies in breastmilk, and there was also the price of baby formula to consider — a one-year supply can cost up to $1,500.

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After some research, Underwood decided to seek out human milk donations. She posted in a milk sharing Facebook group and connected with a Charlottesville resident, who provided Underwood's baby with breastmilk for six months.

"It was absolutely wonderful to be able to have breastmilk,” Underwood said. “It was completely free ... It was out of the kindness of their heart to donate this milk.”

The research is clear: breast is best. Across the Shenandoah Valley and the United States, parents who want their babies to enjoy the benefits of breastmilk but struggle to provide it themselves are turning to human milk donors for help — often through social media. However, some medical professionals caution against the use of unscreened milk, warning that the practice could expose babies to disease and harmful bacteria.

Milk sharing is not a new phenomenon. Women have been breastfeeding other women's babies for thousands of years, mostly as wet nurses. The first human milk bank, which supplied donated breastmilk to sick infants, was established over 100 years ago.

But in recent years, social media has added a modern twist to the practice as milk sharing websites and Facebook pages like Eats on Feets and Human Milk 4 Human Babies, an international network of milk sharing Facebook pages, have given rise to a vast virtual network of breastmilk donors and recipients.

"I definitely think it's gaining traction," said Lauyren Haight, one of the administrators of the Human Milk 4 Human Babies Virginia page on Facebook. "Milk sharing is becoming more widely known."

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Parents seek breastmilk for a range of reasons. Mothers may not be able to produce enough milk, sometimes because of health conditions, and some adoptive parents want to feed their babies breastmilk. Haight said she's seen posts asking for donations for a baby whose mother fell seriously ill or died unexpectedly.

The Virginia milk sharing page sees between five and 10 new posts every day, Haight said. Scrolling through the page is a blur of baby photos, locations, offers and requests: "avocado-free #donormilk needed," "#donormilk needed in Salem, will travel up to 3hrs," "offer: #milk2share available for donation in Sterling."

While some unregulated websites allow people to sell breastmilk, Human Milk 4 Human Babies doesn't permit any monetary exchange — but replacing the donor's milk storage bags is an acceptable and courteous gesture.

Mixing money and breastmilk can be dangerous, incentivizing some sellers to top of breastmilk with other liquids to increase the volume of milk, Haight said. One study found that about 10% of online breastmilk purchases were topped off with cow's milk.

Human Milk 4 Human Babies and other groups like it operate "in the spirit of informed choice," allowing people to make their own decisions based on an understanding of potential risks, benefits and alternative options.

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Parents interested in breastmilk sharing should be aware of a laundry list of possible hazards.

Some infectious diseases, like HIV and hepatitis C, can be transmitted through breastmilk. So can alcohol, illegal drugs and prescription medications. Poorly cleaned breast pumps may contaminate milk with dangerous bacteria, and milk that's been left out too long can go bad. In a study of breastmilk purchased online, researchers found that samples were frequently contaminated with harmful bacteria.

For these reasons, Dr. Ann Kellams, a pediatrician at the University of Virginia Children's Hospital, discourages her patients from accepting breastmilk from unscreened donors. She recommends families purchase milk from a certified bank if possible or ask trusted donors to be tested for infectious diseases.

But Kellams said she understands why this option appeals to many women. They want the best for their children, and breastmilk's positive impacts on babies' immune systems, nutrition and overall health are well-documented. While formula can be beneficial, "it's not a Coke or Pepsi comparison — they're not equal," she said.

"Let's say I had a bilateral mastectomy ... I would be tempted if my sister [said], 'I would give you my milk,'" Kellams said. "But that's my sister, and I know every last thing about her. And if it were a friend, I would probably say, 'I would love to do that. Can I pay for your testing?'"

The risks of informal milk sharing gave Waynesboro resident Megan Leigh pause before she accepted donated milk for her oldest son.

More:A brief history of breastmilk sharing

She wasn't producing enough milk, and his pediatrician said they needed to start using formula. Her son would be labeled "failure to thrive," a broad term for children who don't gain weight like doctors expect, if he didn't put on a few ounces by the next week, the doctor told her at one visit.

Uncomfortable with the idea of formula, Leigh asked the pediatrician, her OB-GYN and lactation consultant about donor milk. The pediatrician and OB-GYN both said she should only use donor milk from a certified bank — where milk can cost up to $8 per ounce, which the single mom couldn't afford — but her lactation consultant was open to discussing the potential risks and benefits of the informal route.

Leigh researched her options and interviewed potential milk donors. She learned about their lifestyles, met their kids and weighed the pros and cons before deciding to take donated milk from a woman she felt she could trust. Still, she always tested the milk with alcohol screening strips before she gave it to her baby.

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"Someone can tell you that they don't do drugs, they don't smoke, they eat healthy, whatever — that doesn't mean that's what actually happens. You want to trust that they would never hurt your kid, but this world is getting a little crazy," Leigh said.

Milk sharing requires a certain amount of faith in humanity. Those who participate have to believe that other women truly just want to help their fellow moms — that, as Leigh said, they would never knowingly hurt another woman's baby.

Advocates of informal milk sharing say this is true for the vast majority of mothers. Some are even willing to go to great lengths for other moms, like driving hours to a pickup location or, in the case of Staunton resident Sarah Wood, using a breast pump just to donate milk.

After the birth of her youngest child, Wood got in touch with a woman who was seeking breastmilk donations via Facebook. Wood could empathize with the mom's plight.

“I had struggled with my first a lot. I was not very knowledgeable with breastfeeding," she said. "I was supplementing him with formula from 4 months to 9 months ... If I had known as much then as I know now, I would’ve nursed him until 2 1/2."

So Wood was more than willing to help a fellow mother — a woman she would never meet in person. She donated more than 300 ounces before the recipient's daughter weaned off breastmilk.

"That's the only reason I was still pumping at that point. I still had a good enough supply that I didn't need to pump just to keep my supply up for my son," Wood said.

Their schedules made it difficult to coordinate a pickup time, so Wood would leave a cooler full of icepacks and frozen breastmilk in the shade in front of her house. They still haven't met in person, but they bonded over the experience and chat occasionally, Wood said.

"Being able to help someone else who was struggling ... it's great," she said.

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Laura Harrison, associate professor of gender and women's studies at Minnesota State University, Mankato, said the difficulties women face in purchasing breastmilk through regulated sources like human milk banks, which are not only expensive but also few and far between in the U.S., could explain why some moms are willing to go to such lengths to support their peers.

"We fail to have this social safety net for women and children's health, so the pressure is put on women to help one another by donating their breastmilk and going to these ... relatively extreme measures in order to assist one another," Harrison said. "I think that sort of speaks to a lack of other options."

Plus, women understand how frustrating and painful breastfeeding can be. Being unable to breastfeed is often heartbreaking, especially for moms who were excited about the experience, Kellams said.

This is why Underwood was willing to drive two hours several times a month to give her spare breastmilk to another mom.

After experiencing so much difficulty breastfeeding her first baby, Underwood was surprised to find that she was an overproducer with her second. She was more than happy to provide some relief for a former coworker who asked if Underwood might be willing to share her spare milk.

“I was able to go full circle and, with the second child, give back,” she said. “It’s been a fun experience.”

Correction: An earlier version of this article misstated the name of Laura Harrison's university. Harrison is a professor at Minnesota State University, Mankato.

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