Raw milk has always been risky to drink. Now a batch has tested positive for bird flu.

Raw milk has been having a moment, with sales rising as much as 65% higher in 2024 compared to 2023. Robert F. Kennedy Jr., President-elect Donald Trump Jr.'s pick to lead the U.S. Department of Health and Human Services (HHS), has promoted raw milk, too, calling for the end of its "aggressive suppression."

But, experts tell Yahoo Life, raw milk is never safe, and least of all now: Bird flu virus was detected in a batch of raw milk from Raw Farm in Fresno, Calif., and recalled, state health department officials announced on Nov. 24. And, just months prior, at least 165 people contracted salmonella after drinking unpasteurized milk from the same farm, Associated Press reported. It was the largest outbreak linked to raw milk in a decade, according to health officials, and nearly 40% of cases involve children under age 5.

The risk of bird flu to humans remains low, according to the Centers for Disease Control and Prevention, thanks in part to pasteurization, which inactivates the virus in the commercial milk supply. But noninfectious fragments of the virus have been detected even in pasteurized milk, raising concerns that untreated milk could pose a greater potential risk to those drinking it.

Even without the potential bird flu risk, experts say that you shouldn’t drink raw milk to begin with. Here's why.

What is raw milk?

The vast majority of milk sold in the U.S. goes through a form of sterilization called pasteurization. During this process, raw milk is briefly heated, killing or inactivating the vast majority of illness-causing bacteria, viruses, mold and other microorganisms.

Raw milk, by contrast, is untreated. Even milk from the healthiest cattle and from the cleanest farms is likely to contain myriad germs that can make you sick, Alex O’Brien, quality coordinator at the Center for Dairy Research, tells Yahoo Life. “You can reduce the risk [via sanitary farm practices] all you want, but it’s always going to be there,” he says. “It’s just the nature of the beast.”

Can raw milk make people sick?

Yes, say experts. “We know that raw milk is a risky food,” says Donald Shaffner, chair of Rutgers University’s food science department. “People that consume milk are subject to food poisoning, including vomiting and diarrhea. If these symptoms are especially bad, people may need to be hospitalized or might even die,” and, he adds, children are likely more susceptible because their immune systems are still developing.

That appears to be the case in largest outbreak of salmonella linked to raw milk in a decade; the average age of the 165 infected people is just 7, Food Safety News reported. More than 90% of those sickened said they drank unpasteurized milk from Raw Farm in Fresno, Calif., and one mother told Fortune she planned to sue the company after three of her children got sick after consuming its products.

While fatalities are rare, five people died from illnesses contracted from raw milk between 2007 and 2020, according to a review of data from the U.S. and Canada. “If you consider the number of outbreaks associated with raw milk in light of the very small amount of milk that is consumed raw, the risk of outbreaks linked to raw milk is at least 150 times greater than the risk of outbreaks linked to pasteurized milk,” the CDC warns on its website.

Raw milk was once a major health issue in the U.S. In 1938, before pasteurization was broadly introduced, milk was responsible for about 25% of all food- and drink-related disease outbreaks, according to the Food and Drug Administration’s 1990 guidance on milk safety. Raw milk is “kind of a wild card; there could be all types of bacteria,” says O’Brien. The most common pathogens found in milk are campylobacter, cryptosporidium, E. coli, listeria, brucella and salmonella, according to the CDC.

Since the introduction of pasteurization, however, milk-related illnesses have become relatively rare. Between 2005 and 2016, only about 9% of food-borne illnesses were attributed to dairy products — and most of those were from raw milk, according to a 2018 study. Those figures were an increase over previous years, as illnesses have risen alongside the popularity of raw milk.

Why are people drinking raw milk?

In recent years, raw milk has become more popular as wellness influencers and public figures such as Gwyneth Paltrow and Robert F. Kennedy Jr. have promoted drinking it and have even encouraged children to consume it. O’Brien suspects that the rise in its popularity is for many a political statement, a way of being “anti-establishment.” He adds that there may be a link to attitudes toward the COVID-19 pandemic, when many Americans became distrustful of shifting guidance from scientists.

Raw milk industry groups “have been propagating what I like to call ‘campfire sciences,’” or guidance based on anecdotal stories claiming that unpasteurized dairy helps with lactose intolerance and allergies related to dairy. Some even say that it has antiviral properties, none of which have been proven, says O’Brien. Nicole Martin, a Cornell University professor of dairy foods microbiology, tells Yahoo Life that “I often hear the argument that pasteurization destroys nutrients and ‘good’ bacteria in raw milk.” But, she explains, the process only reduces the levels of healthy vitamins in raw milk by a small percentage, and you would have to drink impossibly huge quantities of raw milk to obtain any health benefits from so-called good bacteria.

“There simply isn’t a benefit to drinking raw milk that outweighs the risks,” Martin says. Instead, “it’s not a matter of if you’re drinking raw milk you’ll get some kind of contamination, it’s a matter of when,” and the more often you consume it, the more at-risk you are, O’Brien adds.

What about bird flu in raw milk?

H5N1, the virus that causes bird flu, was detected in raw milk sold to consumers for the first time in a batch of Raw Farm’s unpasteurized milk. Though there had been no reports of illness connected to the company’s milk as of Nov. 26, the California Department of Public Health issued a stark warning: “Out of an abundance of caution, and due to the ongoing spread of bird flu in dairy cows, poultry, and sporadic human cases, consumers should not consume any of the affected raw milk,” officials said in a statement. The FDA had previously issued multiple separate warnings against drinking raw milk, noting that inactive pieces of the avian flu virus have been found in about 20% of samples of pasteurized milk. “The virus has been found in high levels in the raw milk from cows infected with the virus, as it appears to have an affinity for the mammary gland,” based on samples tested before going through pasteurization, Martin says. Without undergoing the pasteurization process, it’s theoretically possible that raw milk can contain a live form of the virus that could infect people.

As of Nov. 18, 30 people — mostly farmworkers — have been infected with bird flu after exposure to dairy cows, the CDC said in a statement. All of those infected had mild symptoms, with many reporting eye irritation. So far, the virus has not spread between humans (which would be cause for much greater concern), and health officials still classify the risk to the general public as low.

“There’s not enough data to say yes or no” to whether people can contract bird flu from drinking raw milk, O’Brien says. “But you don’t want to give that virus more time to figure out how to infect humans.”

This article was originally published on May 15, 2024, and has been updated.