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Crustaceans

Crustaceans is entry 2 of the fourteen substances Annex II of Regulation (EU) No 1169/2011 makes declarable. IgE-mediated food allergy, mainly to tropomyosin. Where it hides, which exemptions apply, and what it cross-reacts with.

This is reference information, not a diagnosis and not a treatment plan. A pollen calendar cannot tell you what you are allergic to, and no page can clear a food as safe for you — only the label on the packet in your hand and the clinician who knows your history can do that. Anything beyond mild, short-lived symptoms in the mouth or nose — swelling that affects breathing or swallowing, hives away from the mouth, wheeze, vomiting or faintness — is an emergency question, not a reading question.

What the law says

Annex II, entry 2: “Crustaceans and products thereof”

That wording carries the whole obligation. The substance must be declared whenever it is used in the making of a food and is still present in the finished product, even in an altered form, and it must be picked out inside the ingredient list by typeset — bold, capitals, italics, underlining or a contrasting colour. There is no legal requirement for a separate allergen box, so the ingredient list is where to look.

Source: Regulation (EU) No 1169/2011, Annex II and Article 21 · checked 2026-09-06

What the reaction actually is

Crustacean allergy means prawns, shrimp, crab, lobster, langoustine and crayfish. The dominant allergen is tropomyosin, a muscle protein that is heat-stable, so cooking does not make a crustacean safe and the steam from a boiling pot can be enough to trigger symptoms in a sensitive person. Reactions tend to be immediate and can be severe.

Who gets it, and does it last

Unlike milk and egg allergy, crustacean allergy usually begins in adulthood and usually persists. It is one of the more common causes of food-triggered anaphylaxis in adults across Europe.

Where it hides

• Fish stock, bouillabaisse and seafood soups
• Surimi and crab sticks
• Thai and Vietnamese pastes and curries containing shrimp paste
• Some kimchi
• Prawn crackers
• Glucosamine supplements made from shellfish

The August crayfish party is a fixture in Sweden and Finland, and prawns run through the salads, sandwiches and party food of the whole region. Shellfish stock also turns up in restaurant sauces that are not described as seafood dishes at all, which is the situation worth asking about.

Cross-reactions

Tropomyosin is shared across the arthropods and molluscs, which produces one of the best-known cross-reaction patterns in allergy: crustaceans with molluscs, and both with house dust mite and cockroach. A house dust mite allergic adult who reacts to their first plate of prawns is following a documented route. Crucially, crustacean allergy has nothing to do with fish allergy — they are unrelated animals with unrelated proteins, and "seafood allergy" as a single idea is not a clinical category.

The labelling detail

Crustaceans are entry 2 with no exemptions, so any crustacean-derived ingredient must be declared and emphasised however small the quantity. There is no threshold below which it stops being declarable.

Exemptions: none. Entry 2 has no carve-outs at all, so there is no processed fraction of it that escapes the label.

Precautionary wording — “may contain”, “made in a factory that also handles” — is a separate matter: it is voluntary, unstandardised and carries no threshold. How strictly to treat it is a clinical decision, not a reading of the label. The labelling explainer sets out the whole frame, including what happens in restaurants and bakeries where there is no pack at all.

What gets misread

Two errors matter. Being allergic to prawns does not mean being allergic to fish. And an iodine allergy — or a reaction to iodinated contrast media in a hospital scan — is not caused by shellfish; the belief that it is has been examined repeatedly and has not held up.

Sources: Regulation (EU) No 1169/2011, Annex II · Commission Implementing Regulation (EU) No 828/2014 (gluten claims) · WHO/IUIS Allergen Nomenclature · season windows from the national aerobiology monitoring programmes of Estonia, Finland, Sweden, Denmark and Norway · cross-reaction patterns paraphrased from the allergy literature and EAACI material · checked 2026-09-06

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