Caramel color, added to many soft drinks and some foods to turn them brown, may sound harmless, even appetizing. But in no way does it resemble real caramel. Some types of this artificial coloring contain a potentially carcinogenic chemical called 4-methylimidazole (4-MeI). Under California’s Proposition 65 law, any food or beverage sold in the state that exposes consumers to more than 29 micrograms of 4-MeI per day is supposed to carry a health-warning label. In recent Consumer Reports’ tests, each of the 12-ounce samples of Pepsi One and Malta Goya had more than 29 micrograms per can or bottle. While we cannot say that this violates California’s Prop 65, we believe that these levels are too high, and we have asked the California Attorney General to investigate.

Caramel color is the single most used food coloring in the world, according to a 2013 report from market research firms Mintel and Leatherhead Food Research. “There’s no reason why consumers should be exposed to an avoidable and unnecessary risk that can stem from coloring food brown,” says Urvashi Rangan, Ph.D., toxicologist and executive director of Consumer Reports’ Food Safety & Sustainability Center. “Manufacturers have lower 4-MeI alternatives available to them. Ideally there would be no 4-MeI in food.”

The risks

In 2007, a federal government study concluded that 4-MeI caused cancer in mice and the International Agency for Research on Cancer determined the chemical to be “possibly carcinogenic to humans” in 2011. There’s no federal limit for levels of 4-MeI in foods and beverages, but as of January 7, 2012 California requires manufacturers to label a product sold in the state with a cancer warning if it exposes consumers to more than 29 micrograms of 4-MeI per day. In this case, the exposure comes from consumption.

The California Office of Environmental Health Hazard Assessment used 29 micrograms as the cut off point because that’s the level they determined poses a one in 100,000 risk of cancer””that is, no more than one excess cancer case per 100,000 people who are exposed to that amount daily for a lifetime.

Consumer Reports’ experts think even that risk is too high. “It’s possible to get more than 29 micrograms of 4-MeI in one can of some of the drinks we tested. And even if your choice of soft drink contains half that amount, many people have more than one can per day,” says Rangan. “Given that coloring is deliberately added to foods, the amount of 4-MeI in them should pose a negligible risk, which is defined as no more than one excess cancer case in 1 million people.” To meet that risk level, Consumer Reports’ experts say a soft drink would need to contain about 3 micrograms or less per can.

How we tested

Consumer Reports* tested 81 cans and bottles of various popular brands of soft drinks from five manufacturers between April and September 2013. We purchased the products from stores in California and the New York metropolitan region. In December 2013, we bought and tested 29 new samples, again from the same areas, of those brands that had initially tested above 29 micrograms per can or bottle in either location.

What we found

While our study was not large enough to recommend one brand over another, both rounds of testing found that the level of 4-MeI in the samples of Pepsi One and Malta Goya purchased in both locations exceeded 29 micrograms per can or bottle. The products we purchased in California did not have a cancer-risk warning label.

In our initial testing, some of the other brands we bought in California had average levels around or below 29 micrograms per can, but the New York area samples of those same brands tested much higher. In our second test, though, the levels in the New York samples had come down. For example, regular Pepsi from the New York area averaged 174 micrograms in the first test and 32 micrograms in the second. “The fact that we found lower amounts of 4-MeI in our last round of tests suggests that some manufacturers may be taking steps to reduce levels, which would be a step in the right direction,” says Dr. Rangan

On average, three of the brands””Coke, Diet Coke, and Coke Zero””came in under 5 micrograms per can in our tests, a level Consumer Reports’ experts believe is more acceptable. Sprite, a clear soda that was tested as a control, showed no significant levels of 4-MeI. (See chart below or download a PDF of the chart.)

What manufacturers say

Because California’s regulations took effect two years ago, we contacted PepsiCo and Goya in early January 2014 to ask whether their products sold in California were in compliance with the state’s law. A spokesperson for PepsiCo said in an e-mail, “When the regulatory requirements changed in California, PepsiCo moved immediately to meet the new requirements.” She also said reformulated products containing lower levels of 4-MeI would be available nationwide by February 2014. Goya did not provide a response to our questions.

After we informed PepsiCo of our test results, the company issued a statement that said that Proposition 65 is based on per day exposure and not exposure per can. It also cited government consumption data that shows that the average amount of diet soda consumed by people who drink it is 100 milliliters per day, or less than a third of a 12-ounce can. For that reason, they believe that Pepsi One does not require cancer-risk warning labels””even if the amount of 4-MeI in a single can exceeds 29 micrograms.

Consumer Reports says there is analysis of government data that shows higher levels of daily consumption of soft drinks generally. “No matter how much consumers drink they don’t expect their beverages to have a potential carcinogen in them. And we don’t think 4-MeI should be in foods at all. Our tests of Coke samples show that it is possible to get to much lower levels,” says Rangan.

What Consumer Reports is doing

Based on our results, Consumers Union, the policy and action arm of Consumer Reports, is taking several actions. First, we are alerting the California Attorney General’s office of our test findings regarding Pepsi One and Malta Goya. We are also petitioning the Food and Drug Administration (FDA) to set a federal standard for 4-MeI and in the meantime to require manufacturers to list the type of caramel color they use on their products’ ingredient lists. That’s important because there are four types of caramel coloring. Only the two made with ammonia compounds can contain 4-MeI. However, manufacturers can use the general term “artificial color” interchangeably with “caramel color.” “Europe has labeling requirements and consumers in the United States should have the right to make an informed choice about what they are drinking and eating,” says Dr. Rangan.

In a statement from the agency, the FDA said it does not believe that 4-MeI from caramel color at levels currently in food pose a risk. However, they appreciated Consumer Reports’ tests and are currently doing their own tests of foods, including sodas, for 4-MeI. They are also reviewing new safety data on 4-MeI to determine what, if any, regulatory action needs to be taken.

What you can do

To express your concern about caramel color in food to the FDA, go to Consumers Union’s websiteNotInMyFood.org.

If you want to limit your exposure to 4-MeI, for now the only option is to consume few if any products that list “caramel color” or “artificial color” on their labels. “Clearly, it’s feasible for manufacturers to reduce levels of 4-MeI in their products right now,” says Dr. Rangan. “But until a federal standard is set or there is more transparency in labeling, you may want to read ingredient lists carefully.”