Dye No. 40, also known as Allura red, is the most prevalent dye used in food manufacturing in the United States and is an ingredient in everything from nacho-flavored chips and toaster pastries to fresh-cut meat and breakfast cereal. Even foods that are not pink or red, such as marshmallows and vanilla snack cakes, may have Dye No. 40 (or Red 40) in their ingredient line-up. Many of these foods are particularly appealing to children, and some people have suspected that food dyes lead to attention deficit hyperactivity disorder (ADHD).
Part of the controversy surrounds the fact that food dyes are not a necessary part of food preparation; they are composed of chemicals that aren't essential to a food's taste or texture. Water-soluble artificial dyes, which come in liquid, powder or granule form, are used to reintroduce color removed from foods by processing or cooking. They also change the appearance of foods by making them more appealing to the eye [source: Health].
In September 2010, however, the Food and Drug Administration (FDA) analyzed 35 years of scientific studies and affirmed that color additives don't cause ADHD, though they may increase hyperactivity in some children who already have it. In 2011, the FDA met to discuss the matter again and concluded there was still insufficient evidence of a link between food dyes and ADHD, though they did call for more research. Meanwhile, a British study gave children two drinks with a mix of dyes and then observed them for hyperactivity. Parents noticed an increase in this behavior, but teachers and outside observers did not [source: Fulton].
Still, in Europe, product labels now must list any artificial dyes with a warning that they may cause hyperactivity. There's a movement afoot in the U.S. to make the switch from chemical-based dyes to those made from natural elements, such as vegetables or spices. Food industry experts say these are more costly and less stable [source: Fulton].