Caramel color itself is not classified as a carcinogen, but certain types contain a byproduct called 4-methylimidazole (4-MEI) that the International Agency for Research on Cancer has labeled “possibly carcinogenic to humans.” That distinction matters: not all caramel coloring is the same, and the cancer risk depends on which class of caramel color is used and how much 4-MEI it contains.
Four Classes of Caramel Color
Caramel color is manufactured by heating sugars with different combinations of acids, bases, and salts. The process produces four distinct classes, labeled I through IV. Classes I and II are made without ammonia compounds and contain no detectable 4-MEI. Classes III and IV are manufactured using ammonia or ammonium salts, and this is where the problem compound forms. When sugars react with ammonia under high heat, imidazole compounds are produced as byproducts, and the amount of these compounds increases directly with the ratio of ammonia to sugar used in production.
Classes III and IV happen to be the most commonly used caramel colorings by volume in the food supply. So when you see “caramel color” on an ingredient label, there’s no way to tell which class was used, and therefore no way to know whether 4-MEI is present.
What the Animal Studies Found
The cancer concern traces back to a National Toxicology Program study that fed 4-MEI to rats and mice over two years. The study found “clear evidence of carcinogenic activity” in both male and female mice, based on increased rates of lung tumors. Rats, however, did not develop cancer from the same compound. Based on this split result, IARC classified 4-MEI as a Group 2B carcinogen, meaning there is sufficient evidence of cancer in animals but limited evidence in humans. Group 2B is the “possibly carcinogenic” category, which sits below “probably carcinogenic” (Group 2A) and “carcinogenic to humans” (Group 1).
The key limitation is dose. The mice in these studies consumed far more 4-MEI relative to their body weight than a person would get from food. That’s typical of toxicology studies, which use high doses to detect effects that might be too rare to observe at normal exposure levels. It does not mean normal dietary exposure is safe or dangerous on its own. It means the evidence is incomplete for humans.
Where 4-MEI Shows Up in Food
Cola drinks, coffee, soy sauce, and vinegar consistently show the highest concentrations of 4-MEI in food testing. A systematic review of the research found that dark carbonated beverages averaged around 428 nanograms per milliliter, while light-colored carbonated drinks had none. Soy sauces made with caramel coloring contained some of the highest levels of any food tested, with one study measuring over 3,500 micrograms per kilogram. Coffee is another significant source: instant coffee and coffee substitutes ranged from roughly 200 to over 600 micrograms per kilogram depending on the product.
Some 4-MEI also forms naturally when you cook meat at high temperatures. Beef patties, turkey sausage, pot roast, and gravy all contained small but measurable amounts in testing, though these levels were far lower than what’s found in cola or soy sauce. Belgian research found that for the average person, the biggest sources of 4-MEI exposure were coffee, soft drinks, and beer.
How Regulators Have Responded
Regulatory agencies have taken different approaches. California listed 4-MEI under Proposition 65 and set a threshold of 29 micrograms per day. Any product that exposes consumers to more than this amount requires a cancer warning label. This prompted several major soda manufacturers to reformulate their caramel coloring to reduce 4-MEI levels, specifically for products sold in California.
The FDA has not set a federal limit for 4-MEI. The agency acknowledges that 4-MEI forms in Class III and IV caramel coloring but has not required warning labels or maximum concentration limits at the national level. The European Food Safety Authority took a middle path, establishing an acceptable daily intake for the caramel colorings themselves at 300 milligrams per kilogram of body weight per day as a group. For Class III specifically, EFSA set a lower individual limit of 100 milligrams per kilogram of body weight per day because of separate concerns about immune effects. EFSA concluded that estimated consumer exposure to 4-MEI from caramel color was “not of concern,” though the agency noted that other byproducts in caramel coloring, including furan, may warrant closer attention.
The Immune System Question
Beyond cancer, Class III caramel color contains another compound called THI that suppressed immune function in rats, specifically reducing lymphocyte counts. This effect was most pronounced in animals that were also low in vitamin B6. However, when researchers tested this in a controlled human study using elderly men who were marginally deficient in B6 (a group chosen because they’d be most vulnerable to the effect), seven days of Class III caramel color at the full acceptable daily intake produced no measurable changes in lymphocyte counts, immune cell subsets, or antibody production. The immune concern from animal studies has not translated to humans at realistic exposure levels.
Practical Risk in Context
The honest answer is that caramel color occupies a gray zone. The coloring agent itself is not a carcinogen. The byproduct 4-MEI causes lung tumors in mice at high doses and is classified as possibly carcinogenic to humans, but no human studies have demonstrated a cancer link at the levels people actually consume. The doses that caused cancer in mice were orders of magnitude higher than what you’d get from drinking cola or eating soy sauce.
If you want to minimize exposure, the most practical steps are reducing intake of dark-colored sodas, choosing naturally brewed soy sauce over versions made with caramel coloring, and being aware that instant coffee and coffee substitutes tend to contain more 4-MEI than brewed coffee. You can’t identify which class of caramel color a product uses from the label alone, since all four classes are listed simply as “caramel color” in the United States.