Tree nut allergy affects roughly 1% of Americans, and it tends to stick around. FARE estimates that only about 9% of people outgrow it. It also often comes with other nut allergies. About half of people with tree nut allergy react to more than one kind of tree nut, and 25% to 40% of people with peanut allergy react to at least one tree nut, according to the ACAAI.
Whole nuts are easy to see. The challenge is that tree nuts are often ground into pastes, sauces, and flours, and a dish that has always seemed simple can turn out to contain them. Pesto is a good example.
What Is Pesto, Exactly?
Classic Genovese pesto is a sauce of basil, olive oil, Parmesan, garlic, and pine nuts, ground together into a smooth paste. Many modern versions swap in walnuts, cashews, or almonds to save money or change the flavor. The nuts disappear into the sauce, so the only way to know which ones were used is to ask.
Pine nuts are one of the tree nuts on the FDA's list, so traditional pesto counts.
Where Tree Nuts Hide
- Pesto. Pine nuts, walnuts, cashews, or almonds, depending on the recipe.
- Marzipan and almond paste. Both are made mostly from almonds and show up in cakes, cookies, and holiday candies.
- Praline and nougat. Praline is made from caramelized nuts, often hazelnuts, almonds, or pecans. Nougat often contains almonds or pistachios.
- Chocolate spreads and gianduja. Hazelnut is the main ingredient in many chocolate spreads.
- Baklava and other pastries. Walnuts and pistachios are common fillings.
- Mortadella. FARE notes that this Italian cold cut often contains pistachios.
- Gluten-free baking. Almond flour and other nut flours are popular in gluten-free and grain-free baked goods.
- Nut milks, butters, and oils. Almond milk, cashew cream, and walnut oil all count.
- Sauces and curries. Romesco sauce, many kormas, and some moles are thickened with ground nuts.
- Liqueurs. Some amaretto and hazelnut liqueurs use nuts or nut extracts.
Why It's So Easy to Miss
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Nuts get ground into sauces and flours. Once a nut becomes a paste or powder, it is invisible and often hard to taste.
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The official list changed. In January 2025, the FDA updated its guidance and cut the list of tree nuts that require allergen labeling from 23 to 12: almond, black walnut, Brazil nut, California walnut, cashew, hazelnut (filbert), heartnut, macadamia, pecan, pine nut, pistachio, and English walnut. Coconut, shea, chestnut, and several others were removed. They still have to appear in the ingredient list by name, but they are no longer flagged in the "Contains" line. Older packages may still follow the old list, so you may see both styles for a while.
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Related nuts cross-react strongly. Some pairs share very similar proteins. Most people allergic to cashew also react to pistachio, and most people allergic to walnut react to pecan, according to a 2025 review. Other pairs overlap much less.
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Extracts and flavors vary. Pure almond extract comes from almonds. Imitation almond extract is usually made from benzaldehyde, which is often considered nut-free, but sources vary, so check with your allergist.
Do You Need to Avoid Every Tree Nut?
For years, the standard advice after any tree nut diagnosis was to avoid all of them. That is changing. Many allergists now test nut by nut, since a person allergic to cashew may tolerate almond or macadamia. The ACAAI has reported that many people with peanut allergy avoid tree nuts they could safely eat. If your diet is more restricted than you would like, it is worth asking your allergist whether more targeted testing makes sense.
A few foods sound like nuts and belong to entirely different plant groups. Nutmeg, water chestnut, and butternut squash are unrelated to the tree nuts on the FDA list.
How to Protect Yourself
- Ask which nuts are in the pesto, and whether a sauce is thickened with nuts.
- Be careful with bakery sweets, especially marzipan, praline, nougat, and gluten-free items made with nut flours.
- Check deli meats like mortadella for pistachios.
- Read every label, every time, and remember the list changed in 2025.
- Use ForkSure to scan a dish or package for likely tree nuts. ForkSure flags tree nuts as one of the Big 9.
The Bottom Line
Tree nuts are some of the most versatile ingredients in cooking. They become sauces, flours, sweets, and oils, and in each form they get harder to see. Learning the dishes that traditionally use them, keeping up with the FDA's updated list, and talking with your allergist about exactly which nuts you need to avoid can make eating out simpler and safer.
Stay safe, and when you need help, scan it with ForkSure.