Cross-reactivity guides
If your child reacts to one food, the next question is what else to worry about. These guides answer it the honest way: what genuinely cross-reacts, what only looks alarming on a test, and the shared-protein reason behind each. Grouped by food family and by the protein or syndrome that links them.
By food family
- Food familyCrustacean shellfish cross-reactivityIf you react to one crustacean, you usually react to them all. Why shrimp, crab, lobster, and crayfish are managed as one group, how crustacean shellfish is labeled, why molluscs are a separate and less predictable question, and why fish is not shellfish. Cited.
- Food familyFinned fish cross-reactivityFinned-fish cross-reactivity is high and broad: one fish allergy often means several. Which fish cross-react, how 'fish' is labeled and named by species, why fish is not shellfish, and why some fish are a reason to test, not to assume. Cited.
- Food familyGluten and grain cross-reactivityWheat allergy is not celiac disease and not gluten sensitivity, and the cross-reactivity story differs for each. Which grains cross-react with a wheat allergy (barley and rye yes, oat mostly a contamination question), why gluten-free is not the same as wheat-free, and the protein reason behind it. Cited.
- Food familyLegume cross-reactivityA legume allergy, most often peanut, does not mean avoiding soy, peas, lentils, and chickpeas, because cross-reactivity between peanut and the other legumes is low despite frequent positive tests. The real exceptions are lupin, fenugreek, and the lentil-chickpea-pea triad. Which legumes cross-react, which do not, and why. Cited.
- Food familyMollusc cross-reactivityMollusc cross-reactivity is moderate and uneven, not all-or-nothing. Bivalves, cephalopods, and gastropods, which molluscs cross-react, and the big one: molluscs are not a US major allergen, so they often go unlabeled. How to read the label. Cited.
- Food familySeed cross-reactivitySeed cross-reactivity is not all-or-nothing: sesame is the anchor and the only US major-allergen seed, poppy and sesame can cross-react, and most other seeds are separate allergies to assess on their own. Which seeds travel together, the storage-protein overlap with tree nuts, and the seed-label gap that makes the others hard to spot. Cited.
- Food familyTree nut cross-reactivityTree-nut cross-reactivity is not all-or-nothing. Cashew and pistachio travel together, walnut and pecan travel together, almond is the loner, and coconut is usually fine. Which tree nuts cross-react, which don't, and the storage-protein reason why. Cited.
By shared protein or syndrome
- Shared proteinAlpha-gal syndrome and mammalian meatAlpha-gal is a sugar, not a protein, and you are sensitized to it by a tick bite, not by eating. That is why the reaction to mammalian meat is delayed by hours. Which meats, milk, and gelatin carry it, why poultry and fish do not, and how it is tested. Cited.
- Shared proteinFish parvalbumin cross-reactivityParvalbumin is the shared muscle protein behind finned-fish cross-reactivity. Why one fish allergy often means several, why some fish carry less parvalbumin, and why fish is not shellfish. Cited.
- Shared proteinLTP syndrome (lipid transfer protein cross-reactivity)Lipid transfer proteins (nsLTP) are heat-stable, digestion-stable plant proteins. Unlike the mild PR-10 of oral allergy syndrome, an LTP allergy can be systemic, is often Mediterranean, and is frequently amplified by exercise, NSAIDs, or alcohol. Why a positive LTP test is a serious marker, not a reassuring one. Cited.
- Shared proteinOral allergy syndrome (birch pollen and PR-10 proteins)Oral allergy syndrome is birch pollen cross-reacting with PR-10 proteins in raw apple, hazelnut, soy, peanut, stone fruit, carrot, and celery.
- Shared proteinSeed storage protein cross-reactivitySeed storage proteins (the 2S albumins, 7S vicilins, 11S legumins) are the heat-stable proteins behind the serious, systemic reactions to tree nuts, peanut, sesame, soy, and the legumes. Why a positive storage-protein test is a red flag, which foods truly cross-react, and which only test positive. Cited.
- Shared proteinTropomyosin: shellfish, dust mite, and insect cross-reactivityTropomyosin is the shared muscle protein behind shellfish cross-reactivity. Why one crustacean predicts the others, why molluscs are less predictable, why dust mites are linked, and why fish is not shellfish. Cited.
- Shared proteinWheat-dependent exercise-induced anaphylaxis (WDEIA)In WDEIA, wheat eaten alone is tolerated but wheat plus a cofactor (exercise, NSAIDs, alcohol, infection, menstruation) can trigger anaphylaxis. The marker is omega-5 gliadin. Why it is not ordinary wheat allergy or celiac, and why this is an allergist question.