Which milk contains hormones? Unpacking the facts.

December 20, 2025 •

4 min read

It is a fact that all milk, whether from cows, humans, or other mammals, naturally contains small amounts of hormones. Understanding which milk contains hormones is crucial for consumers navigating the dairy aisle, especially regarding naturally occurring and synthetic versions like rBST.

Quick Summary

All dairy milk contains naturally occurring hormones like estrogen and IGF-1, though at very low levels. The presence of synthetic hormones like rBST is banned in organic milk but may be used in conventional milk, although many brands voluntarily opt out.

Key Points

Natural Hormones: All milk, including cow's and human milk, naturally contains hormones such as estrogen and progesterone.
rBST in Conventional Milk: Many conventional dairy farms have voluntarily stopped using recombinant bovine somatotropin (rBST), and often label their products as "rBST-free" to address consumer concerns.
Organic Milk Standards: USDA certified organic milk guarantees that cows were not treated with synthetic growth hormones like rBST.
Fat Content Matters: Because some hormones are fat-soluble, their concentration is generally higher in full-fat milk and dairy products like butter.
Absorption and Digestion: The human digestive system efficiently breaks down most protein-based hormones found in milk, rendering them inactive and largely negating their potential biological impact.
Health Impact Debate: While many health authorities consider the hormonal levels in milk safe, some controversial studies suggest potential links between high dairy consumption and certain health conditions, with more research needed, particularly for infants and sensitive groups.
Non-Dairy Alternatives: Plant-based milk substitutes provide an option free from animal-specific hormones, though their nutritional profiles can differ significantly from dairy milk.

The Natural Presence of Hormones in Milk

All living organisms, from humans to cows, produce hormones—the chemical messengers that regulate bodily functions. For mammals, this includes hormones involved in reproduction and milk production, which are naturally present in milk. These naturally occurring hormones are a normal and unavoidable component of the milk itself. The human body is designed to digest these protein-based hormones effectively, breaking them down into inactive amino acids.

Naturally occurring hormones found in cow's milk include:

Estrogen: Female sex hormones, which are fat-soluble and therefore more concentrated in full-fat dairy products. Levels are particularly high in milk from pregnant cows, which are often milked during their later stages of gestation in modern dairy farming.
Progesterone: Another female sex steroid hormone. Its concentration is also linked to a cow's reproductive cycle and pregnancy status.
Prolactin: A peptide hormone that stimulates milk production.
Insulin-like Growth Factor-1 (IGF-1): A protein hormone present naturally in all milk. The concentration of IGF-1 in milk is much lower than what is produced by the human body.

The Use of Synthetic Hormones

Beyond natural hormones, some conventional dairy farming practices have included the use of synthetic hormones. The most widely known is recombinant bovine somatotropin (rBST), a synthetic version of the naturally occurring bovine somatotropin (bST). Its purpose is to increase milk production in cows. In the United States, the Food and Drug Administration (FDA) has repeatedly affirmed the safety of milk from rBST-treated cows, concluding there is no significant difference between their milk and that from untreated cows.

However, due to consumer concern, a significant portion of the U.S. dairy industry has voluntarily moved away from using rBST. As a result, many conventional milk brands now carry labels stating they are from "cows not treated with rBST" or "rBST-free".

Conventional vs. Organic Milk: Hormone and Production Differences

To help consumers make an informed choice, this comparison table highlights the key differences related to hormone use and overall production standards between conventional and organic milk.


Feature	Conventional Milk	Organic Milk
Synthetic Growth Hormones (rBST)	Can be used, but many brands are now voluntarily rBST-free and labeled as such.	Prohibited by USDA organic standards. Cows cannot be treated with any synthetic growth hormones.
Naturally Occurring Hormones	Present (e.g., estrogen, progesterone, bST). Levels can be higher if from pregnant cows.	Present (e.g., estrogen, progesterone, bST). As all milk has natural hormones, levels depend on the cow's physiological state.
Antibiotics	Permitted for treating sick cows, with required withdrawal periods before the milk can be sold. Milk is tested for residue.	Prohibited. Preventive care and alternative treatments are used for animal health.
Feed	Can include conventional grains and non-organic supplements.	Must be 100% organic feed.
Outdoor Access	Varies widely by farm; not always required.	Requires at least 120 days of pasture grazing per year, promoting more natural animal behavior.
Labeling	May state "rBST-free," but not required for naturally occurring hormones.	Must be USDA certified and adheres to specific organic regulations regarding hormones and feed.

Impact on Human Health: A Closer Look at the Controversies

While the naturally occurring levels of hormones in milk are low and often broken down by digestion, some concerns and research have explored potential health impacts, especially with high dairy consumption. Key areas of controversy include:

Estrogens in milk and cancer risk: Some epidemiological studies have indicated a potential correlation between high consumption of milk and dairy products and an increased risk of certain cancers, such as prostate, breast, and testicular. This is often linked to the presence of sex hormones, particularly estrogen, which can be higher in milk from pregnant cows. However, the evidence is highly controversial, and other studies suggest dairy intake may reduce cancer risk.
IGF-1 and cancer: Since rBST increases a cow's levels of IGF-1, it is argued that milk from rBST-treated cows may contain higher levels of IGF-1. Some research links high IGF-1 levels to cell proliferation, which is a factor in tumor development. However, the IGF-1 levels found in milk are significantly lower than what the human body produces, and the protein is generally degraded during digestion.
Children and early puberty: Concerns have been raised about the potential effect of milk hormones on childhood development, particularly regarding early puberty. Some studies suggest that the low doses of estrogens in milk could potentially have biological effects in sensitive periods like prepuberty. However, the European Society of Endocrinology notes that there is currently insufficient research to conclude that hormones from cow's milk pose a threat to children's health and development.

The Role of Non-Dairy Alternatives

For those who wish to avoid animal hormones entirely, milk alternatives are widely available. Options like almond, soy, oat, and rice milk do not contain the animal-specific hormones found in dairy. When choosing a non-dairy option, it is important to check the nutritional information, as fortification with vitamins and minerals can vary significantly between brands and types. For soy milk, organic options are recommended to avoid potential genetic engineering.

Conclusion: Choosing What's Right For You

Ultimately, understanding which milk contains hormones is a matter of distinguishing between natural presence and synthetic additives. While all dairy milk contains naturally occurring hormones, organic milk and many conventional brands can assure you that no synthetic growth hormones like rBST were used. The potential health impacts of these hormones from dairy consumption remain a topic of debate in the scientific community, with many experts considering the risk to be minimal for adults.

Your decision should be based on your personal health considerations, ethical preferences regarding farming practices, and dietary needs. The most effective way to choose milk that aligns with your values is to read labels carefully and, if concerned about synthetic hormones, opt for a certified organic or explicitly labeled rBST-free product.

For additional information on dairy safety and production practices, the U.S. Dairy website is an authoritative resource with many articles addressing consumer questions about milk.

Frequently Asked Questions

Yes, all cow's milk naturally contains small amounts of hormones, as they are a natural part of the lactation and reproductive process in all mammals.

The main difference is the use of synthetic growth hormones. Organic milk is produced without synthetic hormones like rBST, while conventional milk may or may not come from cows treated with rBST, though many brands label themselves as 'rBST-free'.

rBST is a synthetic hormone used to increase milk production. The FDA has deemed milk from rBST-treated cows safe, finding no significant difference from milk produced by untreated cows, though consumer apprehension persists.

Yes, the human digestive system effectively breaks down many of the protein-based hormones found in milk, such as bST, into inactive amino acids.

The amount of natural hormones in milk is very low compared to what the human body produces. While most experts consider the effect minimal, some studies suggest potential, though controversial, effects from hormones in milk from pregnant cows.

No milk is truly hormone-free due to natural processes. If your goal is to avoid synthetic hormones like rBST, look for a certified organic product or a conventional milk brand that is specifically labeled as 'rBST-free'.

Plant-based options like almond, oat, or soy milk do not contain the animal-specific hormones found in dairy products. Consumers should check nutritional information as fortification with vitamins and minerals can vary.