A peanut is part of the legume family, although they make up their own branch of the legume family tree. People allergic to peanuts may also be allergic to other legumes. This is called a cross-reaction.

Though cross-reactions are not common, they can be just as dangerous as a reaction to peanuts. Other types of legumes should be avoided by peanut-allergic individuals until a physician has determined whether a cross-reactive condition is present. Peanut-allergic individuals should avoid eating:

• Soybeans
• Peas
• Kidney beans
• Lentils
• Butter beans
• Lima beans
• Chickpeas
• Black-eyed peas
• Green beans

Anyone who has sensitivity to peanuts or other legumes may also be sensitive to unrefined soybean oil, and should avoid the substance.

A peanut allergy should not be confused with a tree nut allergy. Tree nuts are large, edible seeds of trees and include walnuts, cashews, almonds, pecans, Brazil nuts, beechnuts and pistachios. Tree nut allergies are less common than peanut allergies. However, about half of adults who are allergic to peanuts are also allergic to a type of tree nut.

The relationship between different types of nut allergies is not completely understood.  Therefore anyone allergic to peanuts should use caution when consuming tree nuts. Physicians may recommend that patients with peanut allergies also avoid tree nuts as a precaution.

In addition, people with peanut allergies may also be allergic to seeds (e.g., sesame).

Some research suggests that a cross-reaction can occur between peanuts and lupin flour, which is a cooking ingredient that is becoming increasingly popular in pasta and in bread products. Individuals with peanut allergies should avoid any products that contain lupin flour until they have had an allergy test that can confirm or rule out lupin sensitivity.

Some peanut-allergic individuals may find they also have oral allergy syndrome, which is characterized by an itching, tingling or swelling in the lips, tongue, palate or throat after eating certain foods. Usually, this condition involves a relationship between a specific type of food allergy and certain types of pollen (for example, ragweed allergies and oral allergies to ingested bananas and melons often coincide). A cross–sensitivity between the similar proteins found in the food and pollen are usually to blame.