It's not an allergy, as much as the dyes, which are made from petroleum (crude) oil, are harmful.

We put both of our children (son 5 with definite SPD, daughter 2.5, with some sensory issues, possible ADHD) on the Feingold diet which eliminates dyes, artificial flavors, and many preservatives.

We noticed a HUGE difference in our daughter within 4 days. She was cuddly, listening better, had better attention, wasn't so hyper.

We've noticed an improvement in our son as well, but it's a bit harder to tell as he's had some "no no" foods (couple Christmas parties for kids where DH or I forgot to tell them not to give them to him).

At any rate, we're 9 days into the diet and we've seen improvement in both children. But... if you want to follow Feingold (with the preservatives) you NEED to spend the $70 and get the program materials, because you can't tell what foods have preservatives just by reading the label, as many companies use harmful preservatives in their packaging that don't have to be listed on the box etc...