People have used breast milk for reasons other than feeding babies for a very long time. In the first century, Pliny the Elder recommended it for fever, gout and healing from poisonous beetles. In 17th- and 18th-century England and America, breast milk was prescribed for ailments ranging from consumption to blindness.

Today, it is still more than just infant food – though some of its uses are more evidence-based than others.

Historically, the mammary gland has been “highly understudied and underappreciated”, says Lars Bode, a professor and founding director of the Human Milk Institute at University of California San Diego.

There is a stigma around breast milk. The American Academy of Pediatrics observed that mothers in the United States who breastfeed beyond a year often report feeling ridiculed or alienated because of it.

There is still much we don’t know about human milk. Now, researchers are trying to close the knowledge gap.

“Human milk is not made for adults,” says Bode. “But that doesn’t mean that there can’t be potential benefits of certain components of it.”

Why adults drink breast milk

Breast milk has three distinct stages – colostrum, transitional milk and mature milk – and contains fats, proteins, vitamins and minerals. It also has complex sugars called human milk oligosaccharides, which are essential in health and development. (More on those later.) This milk supplies the hormones, stem cells and immune factors, like antibodies and antioxidants, that protect an infant against illness.

But experts doubt a healthy adult would benefit much from breast milk. Any effects are likely to be quite small, explains Katie Hinde, an associate professor at Arizona State University who studies lactation, partly because of the physiological differences between adults and infants. For example, adults have higher stomach acidity, which is “going to break down more of the protective factors in milk”, she says. For most, the ability to effectively digest milk worsens as we age, meaning adults may not be able to absorb beneficial nutrients as well as kids can.

“For your typical healthy adult, I think the effects are likely to be very, very small,” Hinde says. “But it’s possible that people who are vulnerable could potentially benefit from it.”

What’s more, not all milk is the same, making it difficult to predict the benefits for adults. Milk composition varies depending on the environment, the needs of the mother and infant, and the complex dynamic between them. It also changes throughout feeding. This is true across mammal species, says Hinde.

“In that sense, milk is more unique than a fingerprint,” Hinde adds.

Some immunocompromised adults, like cancer patients, have reported feeling relief after consuming breast milk, but more studies are needed to validate this. Early research also suggests specific sugar compounds in breast milk can possibly relieve chemotherapy side-effects.

An adult market for breast milk

Human milk may be complex and understudied, but experts agree on one thing: it’s not safe to drink breast milk bought online from strangers.

“Human milk can be a vector for diseases, and purchasing it from unregulated platforms is setting yourself up to get sick,” says Bode.

And yet, there’s demand. Some people have bought breast milk hoping it will help with athletic gains and erectile dysfunction, though research indicates these outcomes are unlikely. Costs of online breast milk can vary, with some reports putting it at $1.50 an ounce and others at $10 an ounce.

Diane Spatz, a nurse scientist at the Children’s Hospital of Philadelphia and a professor at the University of Pennsylvania, says adult interest in consuming human milk could reflect the growing understanding and messaging of how breast milk influences infant health, like protecting against diseases. That said, there are no research-proven health benefits for adults.

Breast milk as an at-home remedy

It’s not uncommon to find online discussions of alternative uses for breast milk, including in soothing soaps, hair masks or even hangover cures (the latter has been debunked). But while people have used breast milk as an at-home remedy for a long time, its usefulness for various ailments isn’t completely validated by science.

Studies suggest that breast milk might work as a salve for things like burns, sore nipples and rashes – but the results aren’t consistent.

Human milk contains macrophages, a type of white blood cell that kills microorganisms and initiates immune responses. This may be why parents have seen success treating their infant’s minor ear or eye infections with a bit of milk. When milk is fresh, macrophages can “go around and eat up any bacteria that could be on the site”, says Spatz.

But the idea that all breast milk benefits will translate outside feeding a baby is a misconception, Spatz explains. For example, lactoferrin, a protein in breast milk, helps kill bacteria too. But if you freeze or heat human milk, the potency of lactoferrin is reduced – and milk often goes through one of those processes if it’s used for something else later.

If a parent finds themselves with extra milk, Spatz says it’s more than OK to use it in a way that works for your family, like adding it to your baby’s bath to calm their skin. She also says that despite what online videos might suggest, it’s rare for mothers to have an excess of milk.

But if there really is more than enough, there’s another option: donating it to a milk bank, where it will be screened, pasteurized and tested.

Breast milk as a medical treatment

Human milk oligosaccharides (HMOs) are a major component of human milk and have anti-inflammatory effects. These complex sugars help babies develop a healthy gut. Now, scientists are interested in making synthetic versions.

“It’s about understanding why human milk might be potentially beneficial and then using that knowledge to generate new therapeutics or preventatives,” explains Bode.

In a recent study in mice, Bode and his colleagues found one type of HMO helped reduce inflammation and the development of atherosclerosis, a chronic inflammatory disease that can cause heart attack or stroke. Early research also suggests these molecules could help with other conditions, including arthritis, multiple sclerosis and Alzheimer’s disease, says Bode. Other researchers are also studying how HMOs could improve adult gut health. The next stage is to move into human clinical studies.

Breast milk as a ‘liquid biopsy’ for breast cancer risk

Kathleen Arcaro, who leads the breast milk research lab at the University of Massachusetts Amherst, is interested in how breast milk can benefit mothers.

Studying breast milk, she says, “helps us understand individual breast cancer risk and, most importantly, it could give women an opportunity to do something to potentially change that risk”.

Arcaro says breast milk can act as a “liquid biopsy”. It’s a non-invasive method of obtaining breast tissue: just one ounce of milk contains millions of cells, including those that show changes linked to breast cancer risk. Breast milk can also contain signs of inflammation, like cytokines and high sodium. Arcaro and her colleagues are examining whether this inflammation is cancer-promoting and what interventions can help.

Her team also collects breast milk from mothers who tested positive for the BRCA mutation, which can be a signifier of higher risk of breast or ovarian cancers, and evaluates their milk for these related changes.

One day, the hope is that when new mothers come to the hospital for a check-up for their baby, doctors could also take and evaluate a sample of their milk. This would be easy enough to do, Arcaro says.

She says that mothers who donate their milk to Arcaro’s research aren’t surprised that this science is possible. Instead, their typical reaction is: why aren’t we doing this already?