People allergic to certain types of tree nuts may also be allergic to other types of tree nuts – a condition known as a cross-reaction. People allergic to tree nuts may also be allergic to peanuts. Because peanuts are not technically in the same food group (they are a type of legume, not a nut), when both types of allergies occur it is sometimes called coincidental allergies. The relationship between different types of nut allergies, however, is not completely understood. Anyone allergic to tree nuts should use caution when consuming any type of nut or peanuts.  

Some tree nut-allergic individuals may find they also suffer from oral allergy syndrome, which is characterized by an itching, tingling or swelling in the lips, tongue, palate or throat after eating certain foods. Usually, these symptoms occur due to a similarity between a specific type of substance in certain foods (certain fresh fruits and vegetables) and certain types of pollen. For example, melons have been associated with producing oral allergy syndrome in people with ragweed pollen allergies.

Individuals who have exhibited a history of allergies, eczema or asthma are more likely to have a tree nut allergy. These individuals are also more likely to have a severe or life-threatening reaction, such as anaphylactic shock.

Several related conditions may be mistaken for a tree nut allergy. These include:

• Food intolerances. These conditions involve the body’s inability to breakdown specific food substances (such as lactose by people with milk intolerance) – rather than an allergic response to the food in question. With lactose intolerance, for example, a person lacks sufficient amounts of the enzyme lactase, making it difficult to break down the lactose in milk.
  
  
• Food poisoning. Symptoms of food poisoning can also imitate an allergic reaction. But, while the symptoms might appear similar, the body is not producing an actual allergic reaction in these instances. Rather, it is responding to harmful bacteria or other toxins within contaminated or spoiled foods. Reactions can be severe and may therefore be confused with food allergies.
  
  
• Additive sensitivity. Food additives are substances added to food for better preservation, taste and color. Some people have reported experiencing reactions to certain additives when ingested (e.g., MSG, sulfites). More research is needed on this subject before the medical community can confirm or reject this condition.
  
  
• Irritable bowel syndrome (IBS). A disorder in which the large intestine does not function normally, leading to cramping, abdominal pain, bloating, constipation and/or diarrhea. Because specific types of food will sometimes trigger IBS symptoms, this condition may be confused with a tree nut allergy.
  
  
• Other gastrointestinal conditions. Some kinds of cancers and ulcers of the gastrointestinal tract can produce symptoms similar to those experienced with tree nut allergies. These symptoms can include vomiting, diarrhea or cramping abdominal pain that gets worse when eating.
  
  
• Stress or psychological issues. While the relationship between stress and allergy symptoms is not entirely clear, some individuals may feel sick simply by thinking about a certain type of food.