Peanuts are among the most common allergy-causing foods, and they often find their way into things you wouldn't expect. Take chilli, for example, It may be thickened with ground peanuts.
Peanuts aren't actually a true nut; they're a legume (in the same family as peas and lentils). But the proteins in peanuts are similar in structure to those in tree nuts. For this reason, people who are allergic to peanuts can also be allergic to tree nuts, such as almonds, Brazil nuts, walnuts, hazelnuts, macadamia nuts, pistachios, pecans, and cashews.
Sometimes people outgrow some food allergies over time (like milk, egg, soy, and wheat allergies), but peanut and tree nut allergies are lifelong in many people.