I know someone who gets EC lips from wheat allergy or eating wheat. I also have celiac disease which is worse than allergy to wheat since damage is done to your intestines and other areas in body.
There's been information on how something allergic touching your skin can cause reaction elsewhere, but eating things you are allergic to can certainly cause reaction (besides swelling) on lips. Just like people have different side effects from medication, people have different side effects from eating or touching things they are allergic to.
You can't limit the causes of EC since there's other causes. And you may have an allergy you are unaware of.