Are There Growth Hormones in Dairy? A Comprehensive Guide

December 26, 2025 •

4 min read

Fact: All milk naturally contains small amounts of hormones, as is common in many food sources like salmon and celery. But the question of whether there are harmful growth hormones in dairy has been a major point of consumer concern for decades, primarily focusing on a synthetic version.

Quick Summary

All milk naturally contains hormones, with trace amounts of bovine somatotropin (bST). The key distinction lies between naturally occurring bST and the synthetic version, rBST, which is banned in some countries but deemed safe by the FDA.

Key Points

Natural vs. Synthetic: All milk naturally contains bovine somatotropin (bST), but some conventional farmers use a synthetic version called rBST (or rBGH) to increase milk production.
Safety for Humans: Regulatory bodies, including the FDA and WHO, have affirmed that milk from rBST-treated cows is safe for human consumption, as the hormones are broken down by digestion and are species-specific.
Organic Certification: USDA organic standards prohibit the use of synthetic growth hormones like rBST in milk production.
IGF-1 Levels: While milk contains Insulin-like Growth Factor-1 (IGF-1), studies suggest the amount is negligible and orally consumed IGF-1 has minimal biological impact on humans.
Antibiotics and Mastitis: Critics link rBST use to an increased risk of mastitis in cows, potentially leading to greater antibiotic use. However, all milk is tested to ensure it is free of antibiotic residues.

Understanding Hormones in Dairy

For decades, public debate has centered on the presence of hormones in dairy products. This discussion involves both naturally occurring hormones that are inherent to milk and a specific synthetic hormone that has been used in conventional farming. Separating fact from misinformation is essential for making informed dietary choices. It is crucial to recognize that the term "hormone-free" milk is a misnomer, as all living organisms produce hormones naturally.

Natural Hormones vs. Synthetic Growth Hormones (rBST)

All cows, like other mammals, produce a natural protein hormone called bovine somatotropin (bST). This hormone regulates the cow's metabolic processes and is essential for normal growth and milk production. The amount of natural bST found in milk is minuscule, and scientific consensus confirms that it is species-specific and biologically inactive in humans when ingested orally.

In contrast, recombinant bovine somatotropin (rBST), or recombinant bovine growth hormone (rBGH), is a synthetic, lab-produced version of bST used by some conventional dairy farmers to increase milk yield. First approved in the U.S. in 1993, rBST has been controversial. Its use is banned in Canada, the European Union, Australia, and Japan, largely due to concerns over animal welfare, such as increased risk of mastitis in treated cows. When ingested, rBST is also considered biologically inactive in humans and is destroyed by digestion and pasteurization.

The Role of IGF-1 and Estrogens

Beyond bST, milk naturally contains other hormones like Insulin-like Growth Factor-1 (IGF-1) and estrogens. The level of these hormones can vary based on factors such as the cow's lactation cycle and whether she is pregnant.

IGF-1: Bovine IGF-1 is identical in structure to human IGF-1. Although some studies have raised concerns about the potential link between high IGF-1 levels and certain cancers, this is often debated, and regulatory bodies have concluded that orally consumed IGF-1 has minimal impact on human blood levels. The amount consumed in milk is negligible compared to what the human body produces endogenously.
Estrogens: Milk contains small amounts of naturally occurring estrogens, primarily from lactating cows. The concentration can be higher in milk from pregnant cows, which are common in modern dairy farming. However, the human body's own hormone production dwarfs the amount of estrogens consumed through dairy, and digestion further reduces their bioavailability.

Concerns Over Antibiotic Residues

Some critics of rBST point to a potential link between the synthetic hormone and an increased risk of mastitis, a painful udder infection in cows. This, in turn, could lead to a greater use of antibiotics to treat the infections, potentially increasing the risk of antibiotic resistance. However, the U.S. dairy industry maintains a rigorous system of testing all milk for antibiotic residues before it can enter the market, and milk with residue above safe limits is discarded.

Conventional vs. Organic Milk: A Comparison

To help consumers navigate the market, here is a breakdown of the differences, specifically concerning hormones.


Feature	Conventional Milk	Organic Milk
Synthetic Growth Hormones (rBST)	Permitted in the U.S., though many brands now pledge not to use it due to consumer preference.	Prohibited by USDA organic regulations.
Natural Growth Hormones (bST)	Present in trace amounts, as with all milk.	Present in trace amounts, as with all milk.
Antibiotics	Used to treat infections like mastitis, but milk is tested for residues before sale.	Antibiotics are not used in organic-approved treatments. If an animal is treated with antibiotics, its milk cannot be sold as organic.
Animal Welfare	Practices vary significantly by farm.	Adherence to USDA organic animal welfare standards, including year-round outdoor access.
Labeling	May specify "rBST-free" or "not treated with rBST," often with an FDA disclaimer.	Certified with the USDA organic seal, guaranteeing no synthetic growth hormones.

How the Human Body Handles Dairy Hormones

For the vast majority of people, the body's natural processes effectively neutralize the minimal hormones found in milk, whether natural or synthetic. Pasteurization, the heat treatment used to kill harmful bacteria, also denatures about 90% of the bST and rBST present. Any remaining hormones are broken down into inactive protein fragments by digestive enzymes in the gut, just like any other dietary protein. Therefore, concerns that these hormones can directly disrupt the human endocrine system are largely unsubstantiated by mainstream science.

Conclusion

Dairy, like many animal and plant-based foods, naturally contains hormones. The presence of these trace amounts is normal and, in the case of bovine growth hormone (bST), presents no biological activity or risk to human health when consumed. The primary area of contention, the use of synthetic rBST, is a matter of farming practice and consumer preference, not safety, according to major regulatory bodies like the FDA. For consumers who wish to avoid synthetic hormones and have more stringent animal welfare standards, certified organic milk is a widely available option that prohibits their use. The choice between conventional and organic milk is ultimately a personal one, based on your priorities and comfort level with different farming methods.

Is milk from rBST-treated cows safe to drink? See the FDA's position on recombinant bovine somatotropin (bST) here: https://www.fda.gov/animal-veterinary/product-safety-information/bovine-somatotropin-bst

Is milk from cows treated with rBST still nutritious? Yes, numerous scientific studies and the FDA have concluded there is no significant difference in the nutritional quality of milk from rBST-treated and untreated cows.

Frequently Asked Questions

bST is a natural protein hormone produced by cows. rBST, or recombinant bovine somatotropin, is a synthetic version of bST produced in a laboratory, which is injected into cows to increase milk production.

Yes, according to the U.S. Food and Drug Administration (FDA) and other health organizations, milk from cows treated with rBST is safe to drink. The hormone is a protein that is rendered inactive by pasteurization and broken down during human digestion.

Organic milk does not contain synthetic growth hormones like rBST, as their use is prohibited under USDA organic standards. However, all milk, organic included, naturally contains small amounts of bST.

The use of rBST is banned in countries like Canada, Japan, Australia, and throughout the EU, primarily due to animal welfare concerns. These concerns include increased risk of mastitis and other potential health issues for the cows.

IGF-1 is a natural growth factor found in both human and cow's milk. While it has been a subject of research, the amount consumed from dairy is very small relative to what the human body produces and is considered negligible in its effect on human blood levels.

Yes, the pasteurization process denatures or deactivates about 90% of the bovine somatotropin (both natural and synthetic) in milk. The remaining trace amounts are then broken down by digestion.

Many milk products carry a label stating they are from "cows not treated with rBST" or are certified USDA organic. The majority of conventional milk sold today is also from untreated cows, even without a specific label.