Coca-Cola and Pepsi are changing their recipes in the United States, to avoid having to put a cancer warning label on the drinks to comply with California law.
Although the exact formula for the drinks is a closely guarded secret, the caramel colouring in the drinks contains 4-methylimidazole (4-MEI), a chemical that is listed as a carcinogen in California.
Coca-Cola and Pepsi have already altered the recipes of drinks sold in California, to reduce the levels of 4-MEI and avoid the cancer warning labels.
The companies say the changes will be rolled out across the US to make manufacturing the drinks more efficient.
Diana Garza-Giarlante, a spokeswoman for Coca-Cola in the US, told the Associated Press: "While we believe that there is no public health risk that justifies any such change, we did ask our caramel suppliers to take this step so that our products would not be subject to the requirement of a scientifically unfounded warning."
High levels of 4-MEI have been linked to the development of tumours in mice and rats, one study found.
The US Food and Drug Administration (FDA) is currently in the process of reviewing a petition from a US consumer group, the Centre for Science in the Public Interest (CSPI), which wants to ban the use of caramel in food and drink products.
However, FDA spokesman Doug Kras, said: "It is important to understand that a consumer would have to consume well over a thousand cans of soda a day to reach the doses administered in the studies that have shown links to cancer in rodents."
A spokesperson for Coca-Cola in the UK added: "The European Food Safety authority specifically reaffirmed the safety of caramel colouring as recently as March 2011, following a comprehensive review of the literature, and stated that the presence of 4-MEI in caramel colouring is not a health concern.
"The science about 4-MEI in foods or beverages does not support the erroneous allegations that CSPI would like the public to believe.
"The caramel colour in all of our products has been, is and always will be safe. That is a fact."
And added: "In Europe, the caramel manufacturing process by our suppliers remain unchanged and continues to comply with European legislation and safety rules."