Tree nuts

“Tree nuts” is a legal category rather than a botanical one, and the species inside it are not closely related. Almonds are stone fruit seeds. Cashews grow attached to a fruit. Brazil nuts come from a rainforest tree and are not nuts in the botanical sense either.

The law groups them because they share a pattern of allergy, not because they share a family. The US definition names them as a class, giving “almonds, pecans, or walnuts” as examples.

The problem the category creates

Most people allergic to tree nuts are allergic to some of them, not all. Someone who reacts to cashew and pistachio, which are closely related, may eat almonds without difficulty.

That leaves a gap between how the allergy works and how the label describes it. Where a label declares only “tree nuts”, a reader allergic to one species learns nothing about which one is in the product, and has to avoid the whole category.

Where the label names the nut, which many do, the information is precise and useful. Whether you get the name is not something you can rely on in advance.

Peanut is not one of them

Peanut is a legume and is a separate allergen in law, with its own entry in the list. So “nut-free” on a package is an ambiguous claim: it may mean free of tree nuts, free of peanut, or free of both, and none of those is a defined term.

The allergen statement is the precise document here and the front-of-pack claim is not. That is the general pattern on the page for reading labels with a food allergy, and it applies with unusual force to this word.

Coconut, nutmeg and the ones that cause arguments

Coconut is classified as a tree nut for US labelling purposes, which surprises almost everyone including many people with tree nut allergy. Reactions to coconut are uncommon and most people with a tree nut allergy tolerate it, but because of the classification it will be declared.

Nutmeg, water chestnut, shea nut and pine nut occupy various positions depending on the jurisdiction, and pine nut in particular is treated as a tree nut in some markets and not others.

If your allergy is to a specific species, the classification arguments matter less than what your own allergy team has told you to avoid.

Where they appear without looking like nuts

Marzipan and praline are almond. Nougat frequently is. Pesto is traditionally pine nut and often cashew in commercial versions.

Nut oils in cosmetics: almond oil, argan, shea. The highly refined oil exemption in the law applies here as it does to peanut, so a refined nut oil may not be declared as an allergen.

Some plant milks and cheeses, which are cashew or almond based and often positioned as an allergy-friendly alternative to dairy while being a problem for a different allergy entirely.