Corn allergies are considered rare, but they can sometimes be severe. If you have a corn allergy, it means your body doesn't identify corn proteins properly. It thinks they're dangerous, so your immune system releases antibodies to fight off the corn protein. The antibodies trigger a slew of chemicals, including histamine, which cause a variety of allergic symptoms. Possible symptoms are a tingling or itching mouth; hives, eczema or itchy skin; swollen lips, face, tongue or throat; difficulty breathing; congestion; diarrhea, nausea or vomiting; and lightheadedness.

People with corn allergies have to avoid corn and all corn products, including cornstarch and corn syrup. Corn can hide in anything from lunch meats to cereal to candy to baby formula. Many types of starch also contain corn. While food products containing a number of common food allergens have warnings on them, corn isn't usually listed since it's an uncommon allergy. To avoid corn, you have to read ingredient labels.