My son was having more and more violent "tantrums", they came seemingly out of the blue. He was getting violent with me (in retrospect he had quieter tantrums involving biting me (sidenote: being bit on the skin over the shoulder blade is a torture no one should experience) or scratching my face up but that's "all" he was doing in those moments).
I finally, a couple months after he turned 3, watched him go from a happy serene boy to a freaking out, kicking biting head-butting monster, 20 minutes after eating a DumDum lollipop. Once I got him under control (he's tall and I'm short so that just involved my holding him and keeping him from hurting me) he fell fast asleep, which I realized he'd done every other time before.
That day was my "aha" moment, and I thought it was b/c of HFCS. I started doing some reading and found that there are MANY kids and adults out there who cannot handle the stuff. I found out a few months later, when I had the opportunity to read an ingredient list, that there's no HFCS in DumDums, but rather plain old Corn Syrup.
So that meant he can't have corn syrup and I noticed with some other foods (breads! things like that) that HFCS is off limits as well. At
Disneyland when he had a freakout after eating a Dole Whip, I found the ingredient list, and realized that now even corn syrup *solids* were off the list.
It might be food dyes, too, but since most foods without those 3 things also don't have food dyes in them, it's hard to tell. And no one really wants to experiment. Though there was an egg-dying moment when he had a big tantrum, after constantly licking his fingers (he was under 2) while doing the eggs...BUT he was also getting over a nasty nasty cold, and we'd just gotten home from a trip so he was extra tired, and I can't be sure about what caused that problem.
When DS doesn't have those things, he's absolutely fine. Sure he gets angry, but it's NOTHING like what it was when he was eating foods with those ingredients (like Uncrustables, which have corn syrup AND HFCS....those sandwiches, it turns out, were the cause of BAD zoo trips and one nasty evening to a great day at Disneyland, sigh).
Some people have violent reactions to gluten...some even have such reactions to dairy!
It's worth it, VERY worth it, to notice what he has been eating or drinking, before these tantrums. if you can see a common factor, that knowledge will be good. If you eliminate that food or an ingredient and the tantrums go away, you'll know. If they don't go away, then you'll also know.
It's worth it! Best of luck to you!
(oh, and it's not something mystical with the corn syrup, at least in my family...it really seems to be a blood sugar thing...DH monitors his blood sugar, and when he has something with one of those big 3, his glucose level spikes HIGH and FAST, then crashes...when DH has one of those ingredients, he passes out entirely, and osmetimes picks a fight with me before doing so. DS has a violent reaction and then falls asleep. These things do NOT happen with other sugars...cane sugar, cane syrup, tapioca syrup, brown rice syrup...those sugars do NOT do it to them...it's only the corn-based stuff.
Oh, also know that sometimes plain old CORN can do it to a person...we are lucky that it's not all corn for DH and DS, because we love corn and it would have been sad to say goodbye to it. Not to mention, when we're out and he's having pancakes and there's no safe syrup, he has powdered sugar on them...and powdered sugar is cut with corn starch to make it flow...xanthan gum is also corn, as is dextrose...there are countless products made from corn, even Febreze!, so to have an overall problem with corn is nearly as difficult as having a problem with gluten....)