Potassium bromate is a chemical additive used in bread and flour production to strengthen dough and improve the texture of baked goods. Its chemical formula is KBrO3, and in pure form it appears as a white crystalline powder or granules. Despite its widespread use in the United States, potassium bromate has been banned in more than 40 countries, including the EU, UK, Canada, and India, because animal studies have linked it to cancer.
Why It’s Used in Bread
Potassium bromate works as an oxidizing agent in dough. When added to flour, it strips away certain chemical groups on gluten proteins and forces new bonds to form between them. These stronger bonds make the dough more elastic and stable, which translates to better rise in the oven, a finer crumb texture, and a taller, more uniform loaf. Bakers have relied on it for decades because it’s cheap, effective, and acts slowly throughout the entire baking process rather than burning out during mixing.
The FDA classifies potassium bromate as a dough strengthener, flour treating agent, and oxidizing agent. On ingredient labels, you’ll most often see it listed as “potassium bromate” or find the phrase “bromated flour” in the ingredients list. It may also appear under the technical name “bromic acid, potassium salt,” though that’s rare on consumer packaging.
The Cancer Concern
The core safety issue with potassium bromate is that it causes cancer in laboratory animals. Studies in rats have demonstrated that it induces kidney tumors, tumors in the lining of the abdomen, and thyroid tumors. The International Agency for Research on Cancer classifies it as a possible human carcinogen.
The theoretical safety argument is that potassium bromate should convert into potassium bromide, a relatively harmless compound, during the heat of baking. In practice, this conversion is often incomplete. Testing of commercially sold baked goods in Bangladesh found residual bromate levels ranging from undetectable to over 6 mg per kilogram in cakes, with measurable levels also present in breads, burger buns, pizzas, and naan. Insufficient baking temperatures, short baking times, or simply using too much of the additive all leave residues behind. The FDA’s recommended safe threshold for residual bromate in finished bread is just 0.02 mg per kilogram, a level that real-world products frequently exceed.
Kidney Damage and Oxidative Stress
Cancer isn’t the only health concern. Potassium bromate is directly toxic to the kidneys. In animal studies, a single oral dose caused kidney damage severe enough to triple creatinine levels and increase urea levels by 2.5 times, both markers of impaired kidney function. Tissue examination confirmed extensive structural damage to the kidneys.
The underlying mechanism is oxidative stress. Potassium bromate depletes the body’s natural antioxidant defenses, particularly a molecule called glutathione that protects cells from damage. With those defenses lowered, it triggers a cascade of harm: lipid damage in cell membranes increases by 1.5 times, protein damage jumps 2.5 times, and DNA itself sustains direct damage, including abnormal cross-linking between DNA and proteins. This kind of widespread oxidative damage is what drives both the acute kidney toxicity and the longer-term cancer risk.
Where It’s Banned and Where It’s Not
The European Union and the United Kingdom banned potassium bromate in 1990, making them among the first to act on early carcinogenicity data. Canada followed in 1994. Brazil, China, Peru, and Nigeria banned it in subsequent years as evidence accumulated. India joined the list in 2016 after advocacy groups tested commercially sold breads and found bromate residues across multiple brands.
The United States remains one of the few major markets where potassium bromate is still legal. The FDA has not banned it outright but has set limits: concentrations in baked products should not exceed 0.02 mg per kilogram. The agency has encouraged bakers to voluntarily stop using it, but compliance is not mandatory at the federal level.
California became the first U.S. state to take legislative action. In 2023, Governor Gavin Newsom signed Assembly Bill 418, which prohibits any food product manufactured, sold, or distributed in California from containing potassium bromate (along with three other additives). The law takes effect on January 1, 2027, giving manufacturers time to reformulate their products.
How to Spot It on Labels
If you want to avoid potassium bromate, check the ingredients list for “potassium bromate” or “bromated flour.” Some bread brands prominently label their products as “unbromated” on the front of the package, which makes identification easier. Store-brand and budget breads are more likely to contain it than artisan or organic products, though there’s no hard rule. Organic flour cannot contain potassium bromate under USDA organic standards.
Safer Alternatives Exist
The baking industry has viable replacements. Vitamin C (ascorbic acid) is the most widely studied and is considered the safest oxidizing agent available for breadmaking. It works through the same basic mechanism, forming the same strengthening bonds between gluten proteins. The challenge is that vitamin C acts quickly, mostly during mixing, whereas potassium bromate acts slowly throughout the whole process. Bakers have solved this by combining vitamin C with food-grade acids like citric acid or acetic acid, which slow down the reaction and mimic the sustained activity of bromate.
Many large commercial bakeries in the U.S. have already switched. The fact that every bakery in the EU, Canada, and dozens of other countries produces bread without potassium bromate is itself evidence that the alternatives work at scale. The resulting bread may require minor recipe adjustments, but consumers generally can’t tell the difference in the finished product.