Pasteurization does change milk. It reduces certain vitamins, deactivates enzymes, and alters protein structures in ways that lower some of milk’s biological activity. Whether those changes make pasteurized milk “bad” depends on what you’re comparing it to and how much risk you’re willing to accept, because the trade-off for those losses is a dramatically safer product. Here’s what actually happens to milk when it’s heated, and where the real concerns hold up versus where they don’t.
What Pasteurization Does to Vitamins
Heat degrades some of milk’s vitamins. A systematic review and meta-analysis of existing research found statistically significant decreases in vitamins B1, B2, C, and folate after pasteurization. Vitamins B12 and E also dropped, though B6 levels stayed roughly the same. The losses vary depending on the method used. Standard pasteurization heats milk to about 72°C (161°F) for 15 to 30 seconds, while ultra-high temperature (UHT) processing pushes milk to around 135°C (275°F) for a few seconds. The hotter and longer the treatment, the greater the nutrient loss.
That said, milk was never your primary source of vitamin C or folate to begin with. A glass of raw milk contains only about 2 mg of vitamin C, compared to roughly 70 mg in an orange. The vitamins that milk is most valued for, calcium and vitamin D (which is added through fortification, not naturally present at useful levels), are heat-stable and survive pasteurization intact. So the nutrient losses are real but nutritionally minor for most people eating a varied diet.
Protein and Bioactive Changes
This is where the concerns get more interesting. Milk contains bioactive proteins that do more than just provide amino acids. Lactoferrin helps bind iron and has antimicrobial properties. Immunoglobulins (IgA, IgM, IgG) support immune function. These proteins are sensitive to heat.
Research on standard pasteurization shows significant reductions in lactoferrin, IgA, and IgM, though IgG appears to survive better. One study measuring retention of immune proteins after pasteurization at 62.5°C for 30 minutes found that about 72% of IgA survived, but only about 22% of lactoferrin and 39% of lysozyme (an antimicrobial enzyme) made it through. Key milk fat membrane proteins were also significantly reduced. These aren’t trivial losses if you’re drinking milk partly for its biological complexity. For infants receiving donor breast milk, these losses matter most, which is why neonatal researchers actively study gentler pasteurization methods.
For adults drinking cow’s milk, the practical significance is less clear. Most of these bioactive compounds evolved to benefit calves, and their role in adult human health isn’t well established.
Does Pasteurization Make Milk More Allergenic?
One of the more compelling areas of research suggests pasteurization may actually increase milk’s ability to trigger allergic reactions. When the whey proteins alpha-lactalbumin and beta-lactoglobulin are heated, they form aggregates that appear to promote allergic sensitization. In mouse studies, these heated protein aggregates triggered stronger immune responses, including higher levels of IgE antibodies (the type involved in allergic reactions) and increased inflammatory signaling compared to the same proteins in their raw, unheated form.
A human pilot study supported this direction, finding that raw cow’s milk had a lower allergenic potential than processed milk, with the whey protein fraction driving most of the difference. There’s also epidemiological evidence that children who grow up drinking raw milk on farms have lower rates of asthma and allergies, though separating the effect of the milk from other aspects of farm life is difficult. Some researchers have noted that heating can expose new binding sites on beta-lactoglobulin that weren’t accessible before, potentially creating new triggers for sensitized immune systems. The evidence here is genuinely mixed on IgE-binding capacity, but the sensitization data consistently points toward heating increasing allergenic potential.
Enzymes Lost in Pasteurization
Pasteurization inactivates two enzymes in particular: alkaline phosphatase and lipase. In fact, the destruction of alkaline phosphatase is used as the standard test to confirm milk has been properly pasteurized. Lipase normally helps break down fats. Some raw milk advocates argue these enzyme losses make pasteurized milk harder to digest, though there’s limited clinical evidence that bovine milk enzymes play a meaningful role in human digestion, since your own digestive system produces its own lipase in abundance.
One enzyme that does survive standard pasteurization is lactoperoxidase, which has natural antimicrobial properties. This is relevant because it means pasteurized milk retains at least some of its innate defense system against bacterial contamination after opening.
Raw Milk Doesn’t Fix Lactose Intolerance
One of the most persistent claims in raw milk circles is that raw milk is easier to digest for lactose-intolerant people. The theory is that bacteria naturally present in raw milk help break down lactose. A randomized controlled trial tested this directly. Adults with confirmed lactose malabsorption drank raw milk and pasteurized milk on separate occasions, and the researchers measured both hydrogen production (a marker of undigested lactose) and symptom severity.
The result: raw milk did not reduce lactose intolerance symptoms compared to pasteurized milk. Symptom severity was statistically identical between the two. The FDA has also pointed out that raw milk does not contain lactase (the enzyme needed to digest lactose) and does not contain probiotic organisms at the levels found in yogurt, which has actually been shown to help with lactose digestion. Yogurt’s benefit comes from specific bacterial strains deliberately added during manufacturing at concentrations of 10 million or more per milliliter. Raw milk’s natural bacterial population is a different composition at far lower levels.
The Safety Trade-Off
The reason pasteurization exists is foodborne illness. Before it became standard practice, milk was a major vector for tuberculosis, typhoid fever, and other deadly infections. Today, the risk from raw milk is smaller but far from zero. Since 1987, the FDA has documented 143 outbreaks tied to raw milk and raw milk products, involving Listeria, Campylobacter, Salmonella, and E. coli.
A systematic review of outbreaks in the U.S. and Canada from 2007 onward found that two-thirds of dairy-related illness cases came from unpasteurized products. Twenty outbreaks linked to unpasteurized dairy caused 449 confirmed illnesses, 124 hospitalizations, and 5 deaths. Pasteurized dairy outbreaks did occur too (12 outbreaks, 174 confirmed cases), and those that happened tended to be severe because they were overwhelmingly caused by Listeria, which is particularly dangerous for pregnant women and immunocompromised individuals. But these pasteurized-product outbreaks typically involved post-pasteurization contamination or processing failures, not a flaw in the pasteurization process itself.
Raw milk is consumed by a small fraction of the population, so the per-serving risk is disproportionately high compared to pasteurized milk. Children, pregnant women, elderly adults, and anyone with a weakened immune system face the greatest danger.
What This Means Practically
Pasteurized milk is a nutritionally altered version of raw milk. It contains less of certain B vitamins, vitamin C, and folate. It has reduced levels of bioactive proteins like lactoferrin and immunoglobulins. Its whey proteins are structurally changed in ways that may increase allergenic potential. These are legitimate, measurable differences supported by peer-reviewed research.
But the nutrients lost are ones you easily get from other foods. The bioactive proteins lost are of uncertain benefit to adult humans drinking cow’s milk. The lactose intolerance claim doesn’t hold up. And the safety risk of the alternative, raw milk, is well documented and disproportionately falls on the most vulnerable people. If you’re weighing whether pasteurized milk is “bad,” the honest answer is that it’s a trade-off, and for most people the things lost in pasteurization matter less than the pathogens eliminated by it.