4-Methylimidazole (4-MEI) A Fact Sheet

4-Methylimidazole (4-MEI) is a compound used to make certain pharmaceuticals, photographic chemicals, dyes and pigments, cleaning and agricultural chemicals, and rubber products.

4-MEI is formed during the production of certain caramel coloring agents used in many food and drink products. It may also be formed during the cooking, roasting, or other processing of some foods and beverages.

Most people are exposed to 4-MEI by consuming foods and beverages that contain it. Products that potentially contain 4­MEI include certain colas, beers, soy sauces, breads, coffee, and other products.

Workers may also be exposed to 4-MEI if they manufacture certain pharmaceuticals, dyes, and rubber, or if they work with ammoniated livestock feed.

Studies published in 2007 by the federal government’s National Toxicology Program showed that long-term exposure to 4-MEI resulted in increases in lung cancer in male and female mice. These findings were the basis for the addition of 4-MEI to California’s Proposition 65 list of carcinogens.

Exposure to high concentrations of 4-MEI (such as concentrations that might occur in industrial settings) is reported to irritate the lungs or burn the eyes and skin.

Because less is known about exposure to 4-MEI than about exposure to many other chemicals, scientists will continue to study the ways people can be exposed to 4-MEI. The U.S. Food & Drug Administration – which regulates food and beverages – is currently assessing the cancer risk from 4-MEI.

Some caramel colorings used in some soft drinks and other beverages may contain significant amounts of 4-MEI. Cooking, roasting, or other food processing, such as the roasting of coffee beans, may also lead to formation of 4­MEI.

4-MEI is included on California’s Proposition 65 list of substances that can cause cancer. This means that businesses must provide a warning if they manufacture or sell products in California that cause exposures to significant amounts of 4-MEI. Additionally, significant levels of 4-MEI cannot be discharged into sources of drinking water.

OEHHA scientists have developed a “safe harbor” number for 4-MEI, which is a level of exposure that does not cause a significant cancer risk. Products that expose the public to levels of 4-MEI that are less than the safe harbor do not require warnings.

Businesses that do not provide a warning when required, or that discharge the chemical into sources of drinking water, risk civil lawsuits brought by state or local prosecutors or members of the public.