What is Red 40?
Red 40 also known as Allura Red AC is a commonly used artificial food dye.
Red AC is derived from coal tar. 
Synthetic food dyes have been suspected of disrupting children's behavior since the 1970s, when Dr. Ben Feingold, a San Francisco allergist, reported that his patients improved when their diets were changed. Numerous controlled studies conducted over the next three decades in the United States, Europe, and Australia proved that some children’s behavior is worsened by artificial dyes, but the government did nothing to discourage their use and food manufacturers greatly increased their reliance on them.