What is Red 4?
Red 4 is a red azo dye used as a food dye. When used as a food additive, it has the E number E125. It usually comes as a disodium salt. 
It is permitted in fruit peels and maraschino cherries. 
Red 4 is also known as Scarlet GN, or C.I. Food Red 2, Ponceau SX, or C.I. 14700. 
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.