Raw milk isn't safe to drink, experts say. Now it's been linked to 165 cases of salmonella illnesses.

At least 165 people have contracted salmonella after drinking unpasteurized milk from a Fresno, Calif., farm, Raw Farm, the Associated Press reports. It's the largest outbreak linked to raw milk in a decade, according to health officials, and nearly 40% of cases involve children under age 5.

News of the outbreak comes amid growing concern about raw milk, though it’s not stopping some fans of the unpasteurized beverage — including celebrities like former Laguna Beach star and cookbook author Kristin Cavallari — from drinking it. “If I’m going to [drink] milk, it’s going to be raw milk that I get at the farmers’ market,” Cavallari told fans in a clip from her Let’s Be Honest podcast in June.

She’s not alone. Despite repeated warnings from U.S. health agencies, sales of raw milk continue to rise, even amid the ongoing outbreak of bird flu among dairy cattle. In May, it was reported that weekly sales of raw milk had increased by between 21% and 65% compared to the same weeks last year, according to data shared with the Associated Press by NielsenIQ, a market research firm.

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's suing 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?

The FDA has issued a warning against drinking raw milk, given 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,” Martin says. Without undergoing the pasteurization process, it’s theoretically possible that raw milk contains a live form of the virus that could infect people.

However, so far only one person has contracted bird flu from dairy cattle, and that person was a farm worker who was in close contact with the animals. They developed pinkeye but had no other symptoms, and there’s no sign that the worker contracted the virus as a result of drinking raw milk.

“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.