Are there living cells in milk? Unpacking the Science of Raw vs. Pasteurized Dairy

December 13, 2025 •

4 min read

One drop of human breast milk contains over one million white blood cells, a fact highlighting that some milk naturally contains living components. The answer to "Are there living cells in milk?" depends entirely on the type and processing of the milk in question, with a critical distinction existing between raw and commercially treated products.

Quick Summary

The presence of living cells in milk depends on its processing. While raw, unpasteurized milk from mammals like cows and humans contains various living cells, pasteurization kills virtually all cellular life. This contrast has significant implications for understanding milk's composition, quality, and safety.

Key Points

Cellular Presence Varies: The existence of living cells in milk depends on whether it is raw or has undergone heat treatment like pasteurization.
Raw Milk is 'Alive': Raw milk from mammals contains a mix of living immune cells (like white blood cells), epithelial cells, and a natural bacterial microbiome.
Pasteurization Kills Cells: The pasteurization process is specifically designed to kill harmful bacteria and, in doing so, eliminates virtually all living cellular components from the milk.
Somatic Cells in Cow's Milk: Raw cow's milk contains somatic cells (immune and epithelial), and a high count can indicate an infection like mastitis in the cow.
Stem Cells in Human Milk: Human breast milk is especially rich in living immune and stem cells that can be transferred to the baby, aiding in immune system development and tissue repair.
Safety vs. Cellular Content: Pasteurized milk is safer for consumption due to the elimination of pathogens, but it lacks the active cellular components found in raw milk.

The Cellular Composition of Raw Milk

Raw, unprocessed milk contains a dynamic and complex array of living cells, bacteria, and other bioactive components. This is a natural consequence of the milk's origin within a living organism. These cellular components play a functional role, especially in the health of newborn mammals, before heat treatment eliminates their viability.

Living Cells in Human Breast Milk

Human breast milk, often called a "living medicine," is a prime example of this cellular complexity. It is not a sterile fluid but a dynamic, adaptive substance that provides far more than just nutrition. Studies show that human milk contains a multitude of cells that transfer immunity and developmental signals to the infant. The primary types of living cells found include:

Immune cells: Including white blood cells such as macrophages, neutrophils, and lymphocytes. These provide active immunity, helping infants fight infections by consuming pathogens and promoting the development of the infant's own immune system. The concentration of these cells can increase significantly if either the mother or the baby is sick, providing a targeted immune response.
Stem cells: Research has identified the presence of highly plastic stem cells in human milk, which have the potential to differentiate into various cell types, including bone, fat, and neuronal cells. These cells can transfer to the baby during feeding and integrate into their tissues, potentially aiding in organ development and repair.
Epithelial cells: These are shed from the mammary gland itself and are a normal component of milk. They are involved in the process of milk synthesis and are a source of mammary transcripts.
Probiotic bacteria: While not technically mammalian cells, raw human milk contains a diverse microbiome of beneficial bacteria that colonize the infant's gut, promoting digestive health and influencing the development of the immune system.

Living Cells in Raw Cow's Milk

Similarly, raw cow's milk also contains living cells, collectively referred to as somatic cells (SC). These are a mix of white blood cells (leukocytes) and mammary epithelial cells. The somatic cell count (SCC) is a standard measure of milk quality and udder health in dairy cows. In a healthy cow, the SCC is relatively low. However, an elevated SCC, with a higher proportion of white blood cells, is a key indicator of mastitis, an infection of the udder. Like human milk, raw cow's milk also contains bacteria, including both harmless and potentially pathogenic strains.

The Effect of Pasteurization

Pasteurization is a heat treatment process that is critical for ensuring the safety of commercial milk. The process involves heating milk to a specific temperature for a set duration to destroy or deactivate harmful microorganisms and enzymes. This process has a profound effect on the cellular components of milk.

Eliminating Living Cells

The high temperatures used in pasteurization effectively kill the vast majority of living cells found in raw milk, including the immune cells, stem cells, and most bacteria. This means that the commercially available milk found in grocery stores is, for all practical purposes, devoid of any living cells. While the heat treatment destroys the cellular components, it does so with minimal impact on the nutritional quality of the milk, such as its protein, vitamin, and mineral content.

The Exception: Spore-Forming Bacteria

It is important to note that while pasteurization is highly effective, some heat-resistant bacterial spores, such as those from Bacillus and Clostridium species, may survive the process. However, these survivors are in very low numbers and are not considered a threat under normal storage conditions. These heat-resistant bacteria, when present, are in a dormant spore state, not actively dividing living cells in the same way as those found in raw milk.

Raw vs. Pasteurized Milk: A Cellular Comparison


Feature	Raw Milk	Pasteurized Milk
Living Cells Present?	Yes, contains viable immune cells, epithelial cells, and in some species, stem cells.	No, the heat treatment kills virtually all living cells, rendering it non-living.
Immune Cells	Contains active white blood cells (leukocytes) transferred from the mother, offering potential immune benefits.	All immune cells are killed during pasteurization. The milk no longer offers any active immune protection.
Stem Cells	Human milk contains viable stem cells that can transfer to the infant and integrate into tissues.	All stem cells are destroyed by the pasteurization process.
Bacteria	Contains a natural microbiome, which includes both beneficial and potentially harmful bacteria.	Pathogenic bacteria are targeted and eliminated, while some heat-resistant spores may survive but are not active.
Health Implications	Potential benefits (immune support) but also carries risks from pathogens. Risks are higher for vulnerable populations.	Safer due to the elimination of pathogens, but lacks the cellular benefits of raw milk.
Monitoring	Often monitored for somatic cell count (SCC) as an indicator of animal health and potential infection.	SCC and bacterial counts are monitored for quality control, but the cells are not viable.

Conclusion: The Final Verdict

In conclusion, the presence of living cells in milk is determined by its processing. Raw milk from mammals, including cows and humans, is a complex, living fluid filled with active immune cells, epithelial cells, and often, beneficial bacteria and stem cells. These cellular components play significant roles, especially in transferring immunity to newborns. However, for consumer safety, commercial dairy undergoes pasteurization, a heat treatment that effectively eliminates all living cells. Therefore, while raw milk is biologically a "living" substance, the pasteurized milk you buy in the store is not. The choice between raw and pasteurized milk is a trade-off between the potential cellular benefits of the raw product and the guaranteed safety provided by pasteurization.

For more information on the complex components of human milk, see the research summary provided by the National Institutes of Health(https://pmc.ncbi.nlm.nih.gov/articles/PMC5508878/).

Frequently Asked Questions

No, there are no living cells in store-bought pasteurized milk. The pasteurization process involves heating the milk to a high enough temperature to kill virtually all living organisms, including bacteria and any somatic cells from the cow.

Yes, human breast milk is rich in living cells. This includes immune cells (white blood cells) that help the baby fight infections, as well as stem cells that can contribute to infant development and tissue repair.

Raw cow's milk contains living somatic cells, which are primarily immune cells (leukocytes like white blood cells) and mammary epithelial cells shed from the udder. It also contains bacteria, some of which can be pathogenic.

A high SCC in raw cow's milk is often an indicator of an infection, typically mastitis, in the cow's udder. The increase in cells is an immune response to the pathogen.

Pasteurization is designed to kill pathogenic bacteria and significantly reduce other microbial life. While highly effective, some heat-resistant bacterial spores can survive the process, though they are not actively growing.

No. The active, living immune cells and antibodies found in human breast milk are destroyed during the pasteurization process. As a result, pasteurized milk does not offer the same active immune protection.

It depends on the source. While raw human breast milk with its living cells is considered safe and beneficial for infants, raw animal milk with its accompanying bacteria can pose health risks, particularly for vulnerable individuals. Pasteurization eliminates these risks for commercial milk.