Synthetic dyes like Red 40, Yellow 5, and Yellow 6 make foods bright and appealing. A well-known 2007 study from the University of Southampton found that certain artificial color mixtures, combined with the preservative sodium benzoate, increased hyperactivity in some children. The effect doesn't appear in every child, but it's enough that the European Union requires foods with these dyes to carry a label noting they may affect attention in children.
In the U.S. these dyes remain widely used, though scrutiny is growing — a 2021 California state assessment concluded that synthetic food dyes can affect behavior in some children. If your child seems sensitive, choosing products colored with fruit and vegetable extracts is an easy swap.