It depends on the thing...the last time I consumed gluten (which was years ago) I broke out (and became ill) instantly. I get very sick and break out in hives if dried wheat straw even touches my skin or gets in my immediate environment, so I think I must have a severe wheat allergy, not just gluten sensitivity. I've never tested to see if my sensitivity has gone down or gone away over the past few years... I would be interested to know if anything has changed, but due to the fact that in the past I've been sickened for a month or more from even one exposure, I just stay clear of it and plan to for the rest of my life.
Other grains... I've only tested corn so far. I was corn free since 2009 and ate some this past month. Unfortunately I did have a reaction. Cystic acne (when I was previously clear), stomach pains and a rash. The good news is, this reaction didn't appear until I'd eaten corn for three days in a row (at dinner each night). I used to have an immediate reaction to corn the way I did gluten, so it's good to know it has improved a bit. That said, I still won't be eating it, because anything that causes a reaction probably isn't good even in small amounts.
I was able to add rice (brown and white) back into my diet with no problems after being off them for two years. If anything, my skin and overall health improved with the adding of rice.
I am sorry to hear you had such a reaction to wheat/gluten after so long.
Last week I also discovered that corn (and sweet peas/green peas) faired up my childhood eczema, and that corn also made me nauseous if I eat it every day. I haven't eaten corn (or so I think o_0 snce it's in everything) for over two years, and trying it at a picnic last week was an incredible discovery into what other things effect my eczema. I'm sort of a simpler eater and don't dwell on the things I can't have, but after exploring a few other vegetables I haven't had for a long time, I'm shocked at how much I react to them. Reactions are different each time, but they are still reactions. Yet I am not "allergic" to them according to my food allergy test. I'm going back to my GI in a few weeks. He thinks, since the pain is in my bowels and my stools are green whenever something happens, that my food allergens MIGHT be fairing up because of my gut flora possibly being off balance, but he's incredibly skeptical since I have no other pains or symptoms whatsoever on a daily basis and appear overall healthy.
It's confusing, but writing down what happens to you and remembering it will be your best key for great digestion . I hope you can get better with time too!! Maybe one day you'll eat these foods again, who knows?
There's a great blog for corn free items here: http://corn-freefoods.blogspot.com