Hidden Truth of Refrigerated Raw Milk

March 21, 2026

According to a new study, raw milk, which is marketed as a natural and healthful alternative to pasteurised dairy, may contain hidden hazards. The research found that the influenza or flu virus can remain infectious in refrigerated raw milk for up to five days.
The findings come at a time when outbreaks of bird flu in dairy cattle have raised concerns about the potential for a new pandemic. The study was conducted by Stanford University.

“This work highlights the potential risk of avian influenza transmission through consumption of raw milk and the importance of milk pasteurization,” said study senior author Alexandria Boehm, the Richard and Rhoda Goldman Professor of Environmental Studies in the Stanford Doerr School of Sustainability and the Stanford School of Engineering.

More than 14 million Americans consume raw milk annually. Unlike pasteurized milk, raw milk is not heated to kill potentially harmful pathogens. Proponents of raw milk claim that it leaves more beneficial nutrients, enzymes, and probiotics than in pasteurized milk, and can boost immune and gastrointestinal health.

The Food and Drug Administration has tied raw milk to over 200 outbreaks of illnesses, and – together with the Centers for Disease Control and Prevention – warns that germs, such E. coli and Salmonella, in raw milk present “serious” health risks, especially for children, the elderly, pregnant women, and people with weakened immune systems.

The researchers explored the persistence of a strain of human influenza virus in raw cow’s milk at typical refrigeration temperatures. The flu virus, called H1N1 PR8, survived and remained infectious in the milk for up to five days.

“The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways,” said study co-lead author Mengyang Zhang, a postdoctoral scholar in civil and environmental engineering. “The virus could contaminate surfaces and other environmental materials within dairy facilities, posing risks to animals and humans.”

Additionally, the researchers found that flu virus RNA – molecules that carry genetic information but are not considered a health risk – remained detectable in the raw milk for at least 57 days. By comparison, pasteurization completely destroyed infectious influenza in the milk and reduced the amount of viral RNA by almost 90%, but didn’t eliminate the RNA entirely.