Does Heat Destroy Hormones in Milk? A Scientific Analysis

January 1, 2026 •

3 min read

According to a study in the Journal of Dairy Science, heat treatments commonly used in milk processing do not significantly alter concentrations of steroid hormones like estrogen and cortisol. This critical finding helps answer the common question: does heat destroy hormones in milk and, if so, which ones?

Quick Summary

The impact of heat on milk hormones varies by type; protein-based hormones are heat-sensitive, while steroid hormones are heat-stable. Digestion further inactivates most remaining hormone traces.

Key Points

Differential Heat Impact: Heat affects different hormones in milk differently, with protein-based hormones being degraded while steroid-based hormones remain stable.
Pasteurization and Protein Hormones: Pasteurization effectively denatures and destroys a large percentage of protein-based hormones like bovine growth hormone (bGH).
Steroid Hormones Resist Heat: Steroid hormones, including estrogen and cortisol, are robust and resistant to standard heat processing methods like pasteurization.
Digestion Inactivates Hormones: Even if a hormone survives heat treatment, the human digestive system typically breaks it down, rendering it biologically inactive.
Minimal Health Impact: The trace levels of hormones found in all milk are generally not considered to have a significant biological effect on humans, whether the milk is heated or raw.

The Different Types of Hormones in Milk

To understand how heating affects hormones in milk, it's essential to recognize that not all hormones are the same. Milk naturally contains two primary categories of hormones: protein-based hormones and steroid-based hormones. Each type responds differently to temperature changes, which is a key factor in determining their stability during pasteurization.

Protein-Based Hormones: These are hormones composed of amino acid chains, such as bovine growth hormone (bGH), ghrelin, and resistin. Their structure is relatively delicate and can be altered, or denatured, by heat.
Steroid-Based Hormones: These hormones, which include estrogen and cortisol, are derived from cholesterol and possess a stable, ring-like chemical structure. This structural integrity makes them far more resistant to temperature changes.

The Effect of Heat on Specific Milk Hormones

Scientific research has provided detailed insights into how common milk processing temperatures affect various hormones. The results are not uniform across the board.

Protein-Based Hormone Breakdown

Pasteurization and other forms of heat treatment are highly effective at denaturing protein hormones. For instance, studies have shown that 85-90% of bovine growth hormone (bGH) is destroyed during heat treatment. Similarly, research on human milk found that Holder pasteurization, a specific low-temperature, long-duration method, significantly reduced concentrations of ghrelin and resistin. This denaturation breaks down the hormone's structure, rendering it biologically inactive.

Steroid-Based Hormone Stability

In contrast, steroid hormones are robust against typical heat processing. A study published in the Journal of Dairy Science examined the effects of heating milk to 70°C and 95°C and found no significant difference in estrone and 17β-estradiol concentrations compared to raw milk. Another study confirmed that cortisol levels in milk were unaffected by heating at 65°C and 121°C. This stability is a direct result of their hardy chemical composition.

Insulin-like Growth Factor-1 (IGF-1)

IGF-1 is a notable exception. While it is more heat-resistant than bGH, it is still susceptible to breakdown with extensive heat exposure. High-heat processing, such as that used for infant formula, has been shown to break down IGF-1. This is another example of a protein hormone that can be degraded, though it requires more rigorous processing than bGH.

Digestion: The Final Barrier

Even if some hormones survive the heating process, the human digestive system acts as a further safeguard. Like other ingested proteins, any remaining biologically active protein-based hormones are typically broken down into inactive amino acids during digestion before they can be absorbed into the bloodstream. This biological mechanism provides an additional layer of protection against any potential hormonal effects from milk consumption.

Heat vs. Hormonal Type: A Comparison


Hormone Type	Examples	Stability During Pasteurization	Human Digestion Effect	Overall Human Impact
Protein-Based	bGH, Ghrelin, Resistin	Mostly destroyed/denatured	Broken down into amino acids	Negligible
Steroid-Based	Estrogen, Cortisol	Largely stable	Partially absorbed, but low levels pose no risk	Minimal/negligible
Growth Factors	IGF-1	Partially or significantly degraded depending on temperature/duration	Further broken down by digestive enzymes	Negligible

Conclusion: The Final Verdict

So, does heat destroy hormones in milk? The answer is nuanced and depends on the specific hormone. Heat-sensitive protein hormones, like bGH, are largely destroyed during pasteurization, while heat-stable steroid hormones, such as estrogen and cortisol, are not. However, the trace amounts of hormones in milk—whether raw or pasteurized—have been widely determined to have a negligible biological impact on human health, especially once the body's digestive processes are considered. Milk remains a safe and nutritious beverage, with the risk of hormonal interference from consumption being extremely low.

For more detailed scientific data on milk composition and processing, consider reviewing research from the National Institutes of Health (NIH) at https://www.ncbi.nlm.nih.gov/.

Important Takeaways:

Hormone Types Matter: The effect of heat depends on whether the hormone is protein-based or steroid-based.
Pasteurization Breaks Down Protein Hormones: Heating milk effectively denatures protein-based hormones like bGH, rendering them inactive.
Steroid Hormones Withstand Heat: Steroid hormones like estrogen and cortisol are resilient and remain stable through pasteurization.
Digestion Provides an Extra Layer of Safety: The human digestive system further neutralizes any residual hormonal activity.
Overall Impact is Negligible: The minute amount of hormones in milk is not considered biologically relevant to human health.

List of Milk Hormones and Heat Effect:

Bovine Growth Hormone (bGH): Destroyed by heat.
Ghrelin & Resistin: Significantly reduced by pasteurization.
Estrone & Estradiol (Estrogens): Unaffected by heat treatment.
Cortisol: Unaffected by heat treatment.
Insulin-like Growth Factor-1 (IGF-1): Degraded by high heat but more stable than bGH.

Frequently Asked Questions

No, pasteurization does not destroy all hormones. While it can denature heat-sensitive protein hormones like bGH, steroid hormones such as estrogen and cortisol are largely unaffected by the process.

The trace amounts of hormones naturally found in milk, whether raw or pasteurized, are not considered to pose a health risk to humans. The levels are minimal and often rendered inactive by digestion.

Similar to pasteurization, boiling milk would break down protein-based hormones due to the high temperature. However, stable steroid hormones like estrogen and cortisol would likely remain unaffected, as shown by studies using temperatures of 95°C and higher.

All milk contains natural hormones. Some farms use a synthetic version of bovine growth hormone (rBGH) to increase milk production, though this is banned in several countries. Heating affects both natural and synthetic protein hormones similarly, and any remaining traces are broken down by human digestion.

Insulin-like growth factor-1 (IGF-1) is more heat-stable than bGH but can be significantly broken down by extensive heating, particularly the high-heat processes used for infant formula.

Once consumed, any remaining biologically active hormones from milk are broken down by the human digestive system into inactive amino acid components, similar to other proteins.

From a human health perspective, the hormonal difference between heated and raw milk is considered negligible. While raw milk contains more active protein hormones, they are largely broken down during digestion. Heat-stable steroid hormones are present in both.