What's feingold hypothesis?

Unproven ADHD / diet. The 1988 pop claim that food additives or whatever in the diet causes / exacerbates attention-deficit disorder. Since parents both administer the feingold diet and judge its effect, there may be natural to see faces in the clouds or a desired effect; why the many substances all happen to be synthetic doesn't fit with other food hypersensitivities, but some folks claim good results.