The ingredient in question, Red Dye 3, is considered a known carcinogen by the National Institutes of Health (NIH).

"Food dyes, synthesized originally from coal tar and now petroleum, have long been controversial because of safety concerns. Many dyes have been banned because of their adverse effects on laboratory animals or inadequate testing," the NIH website says.

"Red 3 causes cancer in animals, and there is evidence that several other dyes also are carcinogenic."

https://www.thestreet.com/retail/peeps-red-dye-3-cancer