A small number of foods account for most serious food allergies: peanuts, nuts that grow on trees, milk, eggs, wheat, soya, fish, shellfish and sesame among them. Which of those appear on a country's official list varies, and so do the rules about declaring them.
Celery, mustard, lupin, molluscs and sulphites join that list in parts of Europe, which is a useful reminder that an allergen list is a legal instrument as much as a biological one. A food can be declared in one country and invisible in another.
The obvious form of a food is rarely the problem. Peanut turns up as an oil and as a thickener; milk turns up as casein and whey in things nobody thinks of as dairy; egg turns up as a glaze on a loaf and as the binder in a burger.
Wheat hides in soy sauce. Fish hides in Worcestershire sauce and in some kimchi. Sesame hides in bread, in hummus as tahini, and in the seed mix on a bun that nobody thought to call a seeded bun.
Wheat and gluten are not two words for one thing, and a gluten-free label is a claim about gluten rather than about wheat. Somebody avoiding wheat because of an allergy and somebody avoiding gluten because of coeliac disease are reading the same label for different reasons.
Labels are the best tool available and they are not a complete one. An ingredients list declares what was put in on purpose; it says nothing reliable about what else was in the room. The precautionary wording that follows the list is a separate matter, and it has its own page here.
This page is background knowledge, not a decision tool. Knowing that sesame hides in bread does not settle whether a particular loaf on a particular counter is a problem for a particular person. Only the kitchen that made it, and that person's own doctor, can get near that.
Names change between languages and between countries, and the same ingredient can be listed under a term the reader has never seen. That is why a translated card names the allergen in the local language rather than trusting a traveller to recognise it on a label.
The list is not a ranking either. A food low on any chart of common allergens is exactly as serious for the person who reacts to it, and an unusual allergen is not a mild one.
Questions this page raises
Ezzie will have a go at any of these.