Back in 1976, Red Dye #2 was banned from the use of food after being discovered to be carcinogenic. This was the key food color used to in M&M’s colorful snacks. But, when the dye was reintroduced into food products in 1983, M&M jumped right back into its use, much to the dismay of their consumers.
Apart from Red Dye #2, M&M’s contain:
Blue Dye #1: linked to malignant tumor growth in rat studies as well as low blood pressure problems, hives, asthma, and allergic reactions
Blue Dye #2: linked to tumor growth, abnormal cell development, and hyperactivity in children
Red Dye #40: linked to cancer, DNA damage, swelling around the mouth, hives, and hyperactivity
Yellow Dye #5: a common food allergy, as well as potential links to cancer and behavioral problems
Yellow Dye #6: linked to diarrhea, vomiting, migraines, allergic reactions, hyperactivity and cancer