There’s a high degree of cross-reactivity between cashew and pistachio and between walnut, hazelnut, and pecan, so some healthcare professionals may advise you to avoid all tree nuts even if you only have a confirmed allergy to one.

There’s also a high degree of cross-reactivity between different fish species, so healthcare professionals may advise their fish-allergic patients to avoid all fish.

And studies have found that the risk of an allergic reaction to goat's milk or sheep's milk in a person with a cow’s milk allergy is about 90%.