: Is it possible to be allergic to corn but not popcorn? Is it possible for a person to be allergic to one subspecies and not another of the same parent species? For instance, can a person be allergic to sweet corn but not

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Essentially this depends on which specific protein a person is allergic too. There will be a lot of crossover in plants so closely related as to be different subspecies of the same species, but some proteins may be unique.

Following your example of corn, this is taken from an interesting 2012 paper on the Molecular Features of Maize Allergens and their Implications in Human Health:

Detailed biochemical knowledge of maize allergy is lacking. There are several unanswered questions including the symptoms and mechanisms involved in maize allergenic reactions, its prevalence in adults and children, the implicated allergen molecules and the clinical cross-sensitization. Therefore, diagnostic tests and maize allergy management constitute a field of great interest. Currently, maize allergen proteins are classified into 20 different families, displaying diverse structures and functions. They are responsible for many IgE cross-reactions between unrelated pollen and plant food allergen sources. The most relevant maize allergen molecules belong to the Expansin and the Ole e 1 superfamilies, the panallergen Profilin, and the Lipid Transfer Proteins (LTPs), i.e. Zea m 14, the major maize allergen.

This is clearly a complex area, with ongoing research.

You mention sweet corn vs popping corn, which are different subspecies of Zea mays. Interestingly, sweet corn is sweet because of a recessive mutation that reduces the conversion of sugar to starch.

Heating a food can denature proteins, reducing their bio activity. It is possible that the act of popping corn might reduce allergenicity somewhat.

In a Review of Food Processing and Allergenicity, peanuts, tree nuts, cows' milk, hens' eggs, soy, wheat and mustard were reviewed. It was found that:

Processing may influence, but does not abolish, the allergenic potential of proteins.
Reduction of allergenicity by fermentation and hydrolysis are the best characterised.

Cross-reactivity

There is also cross-reactivity, in which allergy to one protein results in an allergy to another similar protein in a completely different species (e.g. apples and birch pollen). This results in types of allergy like oral allergy syndrome.

All allergies are mediated by an immune system dysfunction known as type 1 hypersensitivity. Other types of hypersensitivity are responsible for other reactions and autoimmune conditions.