rBST (recombinant bovine somatotropin) is a synthetic version of a growth hormone naturally produced by cows. Dairy farmers inject it into cows to boost milk production, and that milk can then be used to make cheese, yogurt, and other dairy products. You’ve likely seen it on cheese labels because many brands now advertise “from cows not treated with rBST” as a selling point.
How rBST Works in Dairy Cows
Cows naturally produce a hormone called bovine somatotropin (bST) in their pituitary gland. This hormone helps regulate how much milk they produce. rBST is a lab-made copy of that natural hormone. When injected into dairy cows, it signals their bodies to produce more milk from the same amount of feed. The FDA approved the product in 1993 under the brand name Posilac after determining it was safe and effective.
At its peak, rBST was widely used across the U.S. dairy industry, but adoption has dropped significantly. A USDA survey in 2014 found fewer than 1 in 6 dairy cows were receiving rBST injections, and usage has continued declining since then as consumer demand shifted toward rBST-free products.
Does rBST End Up in Your Cheese?
Not in any meaningful way. bST is a protein, and like most proteins, it breaks down when exposed to heat and digestive enzymes. Pasteurization destroys it to a large extent, and the cheesemaking process (which involves heat, bacterial cultures, and aging) breaks it down further. Research from Canada’s Parliamentary Research Branch confirmed that both rBST and a related growth factor called IGF-1 are destroyed during yogurt production, and similar degradation occurs during cheese production.
Even if trace amounts survived processing, bST has no biological activity in humans. It’s a cow-specific hormone. The FDA’s safety assessment emphasized that even if bST were injected directly into a person, it wouldn’t do anything because growth hormones from cows don’t activate human biological pathways. When consumed orally, digestive enzymes in your gut break it into inactive fragments.
The IGF-1 Question
The more nuanced concern has never really been about rBST itself, but about IGF-1 (insulin-like growth factor 1), a compound that increases slightly in milk from rBST-treated cows. IGF-1 exists naturally in all cow’s milk, and higher levels of IGF-1 circulating in the human body have been loosely associated with certain cancers in some epidemiological studies. That connection raised questions about whether drinking milk with elevated IGF-1 could be a risk.
The evidence has been reassuring on this point. The IGF-1 concentrations in milk from rBST-treated cows fall within the normal range that varies naturally between farms, seasons, and stages of a cow’s lactation cycle. Your own digestive tract produces far more IGF-1 than you’d ever consume from milk or cheese. Studies on oral consumption of IGF-1 in humans have shown it has little to no biological activity when it passes through the gut.
Why Labels Say “No Significant Difference”
If you read the fine print on cheese or milk labeled “from cows not treated with rBST,” you’ll almost always find a disclaimer stating something like: “No significant difference has been shown between milk from rBST-treated and non-treated cows.” That language exists because the FDA determined there is no compositional difference between the two types of milk that would justify mandatory labeling. The agency concluded it didn’t have the legal authority to require special labels since the milk is essentially the same product.
Companies can voluntarily label their products as rBST-free, but the FDA’s guidance asks them to include that disclaimer so consumers aren’t misled into thinking rBST-free milk is nutritionally or safety-wise superior.
Animal Welfare Concerns
The strongest scientific case against rBST has always been about the cows, not the consumers. A large meta-analysis published in the Canadian Journal of Veterinary Research found that rBST-treated cows had roughly a 25% higher risk of developing mastitis (a painful udder infection) during the treatment period. Across a full lactation, that translated to about a 19% increase in total mastitis cases per cow. Treated cows also had an estimated 50% higher risk of clinical lameness.
These animal health effects are the primary reason the European Union permanently banned rBST use in 1999, citing animal welfare. Canada, Australia, New Zealand, and Japan have also prohibited it. Notably, the EU still allows imports of dairy products from countries where rBST is used, which signals that the concern is about how the cows are treated rather than about the safety of the resulting milk or cheese.
What This Means for Choosing Cheese
From a food safety standpoint, cheese made from rBST-treated cow’s milk is not chemically different from cheese made without it in any way that affects your health. The hormone breaks down during processing, and even intact bST has no effect on human biology. The IGF-1 levels fall within natural variation.
The reason many people still choose rBST-free cheese comes down to animal welfare and broader preferences about how food is produced. If those concerns matter to you, look for labels that specifically state “rBST-free” or “from cows not treated with rBST.” Organic cheese is always rBST-free by definition, since USDA organic standards prohibit synthetic hormones. With rBST use already below 15% of U.S. dairy cows and still declining, most conventional cheese on store shelves today likely comes from untreated cows regardless of what the label says.