It seems there is such thing, but it’s rare for corn in particular. In the case of someone who does eat corn and break out in hives or a rash, obvious symptoms, it is quite real.
I think the nonsense and woo-woo part comes in to play when people who experience “chronic fatigue” announce it is due to a corn allergy that has never been diagnosed by a doctor, just something they read online. Or parents whose children have a serious condition like Autism, starting reading strange “natural healing” books who advise them it is due to a corn or wheat or gluten allergy, and say their children’s behavior will be cured by eliminating allergic foods, or claim their intelligence and grades will improve if they stop giving them milk to drink.
These kids never had a rash, hives, swelling or actual signs of a true allergic reaction. I think it’s sometimes a case of “Moms Gone Overboard.”
Since I’ve posted the thread I had a chance to speak with my pediatrician further regarding the food allergy claims. She said there is a simple blood test that can help to detect food allergies. She also said that dozens and dozens of mothers with perfectly healthy kids demand the test with no reason to, and if there is the slightest result that would normally mean people could still eat the food without any problems, some of these parents immediately put their kids on strict diets eliminating the food altogether.