Coke and Pepsi said on Friday that they had asked their suppliers of the caramel coloring in their colas to alter their manufacturing process to meet the requirements of a California ballot initiative aiming to limit people's exposure to toxic chemicals and also to avoid the need to label the packages with a cancer warning.
The change will not be noticeable to consumers, according to statements from both companies.
"Consumers will notice no difference in our products and have no reason at all for any health concerns," said PepsiCo spokeswoman Gina Anderson in a statement.
The change is meant to reduce the amount of a chemical called 4-methylimidazole, or 4-MI, which in January was added to the list of chemicals covered by California's Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65.
High levels of that chemical have been linked to cancer in animals.
The California statute says that "no person in the course of doing business shall knowingly and intentionally expose any individual to a chemical known to the state to cause cancer or reproductive toxicity without first giving a clear and reasonable warning ..."
Coca-Cola spokesman Ben Sheidler said the modification to the manufacturing process will have no effect on the formula, color or taste of Coca-Cola.
Both companies said they started in California, and would expand the use of the reduced 4-MI caramel coloring over time.
Dr Pepper Snapple Group Inc said all the caramel color being produced for it meets the new California standard.
Earlier this week, the Center for Science in the Public Interest (CSPI), a U.S. watchdog group, said it found unsafe levels of the chemical in cans of Coca-Cola, Pepsi-Cola, Dr Pepper and Whole Foods Markets Inc's 365 Cola.
The U.S. Food and Drug Administration said at the time it was reviewing the group's petition but stressed that the drinks were still safe. An FDA spokesman said a person would have to drink "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".
Shares of Coke and Pepsi were both up less than 1 per cent in afternoon trade, roughly in line with the Standard & Poor's 500 index. Dr Pepper Snapple shares were up 1.1 per cent at $38.12.