Peanut & Tree Nut Allergy: Symptoms, Treatment & Prevention

What Is Peanut and Tree Nut Allergy?

Peanut allergy and tree nut allergy are immune system overreactions to proteins found in peanuts and tree nuts. When someone with these allergies eats even a tiny amount of the allergenic food, their immune system releases chemicals like histamine that cause symptoms ranging from mild itching to life-threatening anaphylaxis.

Food allergies occur when the immune system mistakenly identifies certain food proteins as harmful invaders. In the case of peanut and tree nut allergies, the body produces immunoglobulin E (IgE) antibodies against specific proteins in these foods. Upon subsequent exposure, these antibodies trigger mast cells and basophils to release inflammatory mediators, causing allergic symptoms.

Despite the common terminology, peanuts and tree nuts are botanically distinct. Peanuts (Arachis hypogaea) are legumes that grow underground, related to beans, lentils, and soybeans. Tree nuts, in contrast, are the edible seeds of trees and include almonds, walnuts, cashews, pistachios, hazelnuts, pecans, Brazil nuts, and macadamia nuts. This botanical difference is clinically significant because being allergic to peanuts does not automatically mean you are allergic to tree nuts, though approximately 25-40% of individuals with peanut allergy also demonstrate sensitization to at least one tree nut.

Peanut allergy is one of the most common food allergies worldwide, affecting approximately 1-3% of children in Western countries. The prevalence has been increasing over the past several decades, though the exact reasons remain under investigation. Tree nut allergy affects roughly 1% of the general population. Together, peanut and tree nut allergies account for the majority of fatal and near-fatal food-induced anaphylaxis cases, making them a significant public health concern.

True Allergy vs. Cross-Reactivity

Cross-reactivity occurs when the immune system reacts to proteins that are structurally similar to the original allergen. People with pollen allergies, particularly birch pollen allergy, may experience oral allergy syndrome (OAS) when eating peanuts or tree nuts due to proteins that resemble birch pollen allergens. This cross-reactivity typically causes mild symptoms limited to the mouth and throat because the cross-reactive proteins are quickly degraded during digestion.

True peanut or tree nut allergy involves sensitization to stable storage proteins (such as Ara h 1, 2, and 3 in peanuts) that survive digestion and can cause systemic reactions. Understanding whether you have true allergy versus cross-reactivity is important for risk assessment and management, and requires proper allergy testing.

What Are the Symptoms of Peanut and Tree Nut Allergy?

Symptoms of peanut and tree nut allergy typically appear within minutes of exposure, usually within 30 minutes. They can range from mild (itching, hives, tingling mouth) to severe (difficulty breathing, throat swelling, dizziness, loss of consciousness). Anaphylaxis is a life-threatening reaction requiring immediate epinephrine.

Allergic reactions to peanuts and tree nuts can affect multiple organ systems and vary widely in severity. The speed of symptom onset and the number of body systems involved are important indicators of reaction severity. Mild reactions may involve only one organ system (such as skin), while severe reactions typically affect multiple systems simultaneously.

The unpredictable nature of peanut and tree nut allergies is a key concern. A person who has previously experienced only mild reactions can potentially have a severe reaction upon subsequent exposure. Factors that may increase reaction severity include the amount of allergen consumed, whether the person has asthma (particularly poorly controlled asthma), and whether they exercised around the time of exposure.

Skin Symptoms

Skin reactions are the most common manifestations of peanut and tree nut allergy, occurring in approximately 80-90% of allergic reactions. These symptoms typically appear within minutes and may include widespread hives (urticaria), which are raised, itchy welts that can appear anywhere on the body. The affected person may also experience intense itching (pruritus), redness and flushing of the skin, and swelling (angioedema), particularly around the eyes, lips, and face. Eczema flares can also occur in individuals with atopic dermatitis.

Gastrointestinal Symptoms

Digestive system symptoms affect approximately 30-40% of individuals during allergic reactions. These include nausea and vomiting, abdominal pain and cramping, and diarrhea. The person may also experience difficulty swallowing due to throat or esophageal swelling. In young children, gastrointestinal symptoms may be the primary or only manifestation of food allergy.

Respiratory Symptoms

Respiratory symptoms are particularly concerning as they can indicate a severe reaction. These include nasal congestion and runny nose, sneezing, coughing, wheezing, shortness of breath, throat tightness, and difficulty breathing. Voice changes or hoarseness may indicate laryngeal edema, a serious sign requiring immediate treatment.

What Causes Peanut and Tree Nut Allergy?

Peanut and tree nut allergies develop when the immune system incorrectly identifies specific proteins as threats. Risk factors include family history of allergies, having eczema or other food allergies, and possibly delayed introduction of peanuts in infancy. The exact cause is a combination of genetic predisposition and environmental factors.

The development of food allergies, including peanut and tree nut allergies, involves a complex interplay between genetic susceptibility, immune system function, and environmental exposures. Understanding these factors is crucial for both prevention and management of these conditions.

At the molecular level, allergic sensitization occurs when the immune system encounters food proteins and mistakenly categorizes them as harmful. This leads to the production of allergen-specific IgE antibodies that attach to mast cells and basophils throughout the body. Upon subsequent exposure to the same food proteins, these IgE antibodies recognize the allergen and trigger the release of histamine and other inflammatory mediators, causing allergic symptoms.

Genetic Factors

Family history is one of the strongest predictors of food allergy development. If one parent has any allergic condition (food allergy, asthma, eczema, or allergic rhinitis), the child has a 40-50% increased risk of developing allergies. If both parents are affected, this risk increases to 60-80%. Specific genetic variants affecting immune regulation, skin barrier function (such as filaggrin gene mutations), and IgE production have been associated with increased food allergy risk.

The Atopic March

Many children with food allergies follow a pattern called the "atopic march," where eczema (atopic dermatitis) appears first in infancy, followed by food allergies, then later by asthma and allergic rhinitis. Having eczema significantly increases the risk of developing food allergies, possibly because damaged skin allows food proteins to enter the body and trigger sensitization. This theory, known as dual allergen exposure hypothesis, suggests that early skin exposure to food allergens in the presence of a disrupted skin barrier promotes allergic sensitization, while early oral exposure promotes tolerance.

Environmental Factors

Environmental factors influencing peanut and tree nut allergy development include timing of allergen introduction (delayed introduction may increase risk), gut microbiome composition, vitamin D status, and dietary factors affecting immune development. The "hygiene hypothesis" suggests that reduced exposure to diverse microbes in modern environments may contribute to increased allergy rates, though this theory continues to be refined by ongoing research.

How Is Peanut and Tree Nut Allergy Diagnosed?

Diagnosis involves detailed history-taking, skin prick tests, specific IgE blood tests, and sometimes oral food challenges. The oral food challenge is considered the gold standard for diagnosis. Component-resolved diagnostics can help determine the severity of allergy and likelihood of outgrowing it.

Accurate diagnosis of peanut and tree nut allergy is essential for appropriate management and avoiding unnecessary dietary restrictions. The diagnostic process typically involves multiple steps, combining clinical history with objective testing. Importantly, sensitization (positive test result) does not always equate to clinical allergy (actually having symptoms when eating the food).

Medical History

The diagnostic process begins with a thorough medical history. Your allergist will ask detailed questions about the suspected allergic reaction, including what foods were eaten, how soon after eating symptoms appeared, what specific symptoms occurred, how long symptoms lasted, what treatment was needed, and whether similar reactions have occurred before. Information about other allergies, eczema, asthma, and family history of allergic conditions is also important.

Skin Prick Testing

Skin prick tests involve placing a small drop of allergen extract on the skin (usually the forearm or back) and making a tiny prick to allow the allergen to enter the superficial skin layer. If you are allergic, a raised, red, itchy bump (wheal) will appear within 15-20 minutes. Skin prick tests are rapid and relatively inexpensive, but a positive result indicates sensitization, not necessarily clinical allergy. False positives are common, especially in people with eczema or dermatographism.

Blood Tests (Specific IgE)

Blood tests measure the levels of allergen-specific IgE antibodies in the blood. These tests can be performed regardless of skin conditions or antihistamine use. Like skin tests, they indicate sensitization rather than clinical allergy. Component-resolved diagnostics (CRD) can identify IgE antibodies to specific proteins within an allergen. For peanut, this includes Ara h 1, 2, 3, 6, 8, and 9. Sensitization to Ara h 2 is particularly associated with more severe clinical reactions.

Oral Food Challenge

The oral food challenge (OFC) is considered the gold standard for food allergy diagnosis. During an OFC, gradually increasing amounts of the suspected allergenic food are given under medical supervision while monitoring for reactions. This test definitively determines whether clinical allergy exists and can establish the threshold at which reactions occur. OFCs should only be performed by trained allergists with appropriate emergency equipment and medications available.

How Is Peanut and Tree Nut Allergy Treated?

The primary treatment for peanut and tree nut allergy is strict avoidance of the allergenic food. For accidental exposures, antihistamines treat mild symptoms while epinephrine (adrenaline) auto-injectors are essential for severe reactions. Oral immunotherapy (OIT) is an emerging treatment that can increase tolerance thresholds in some patients.

Management of peanut and tree nut allergy has traditionally focused on allergen avoidance and emergency preparedness. However, the treatment landscape is evolving with the development of desensitization therapies. A comprehensive management approach involves education, vigilant avoidance, emergency action planning, and potentially newer therapeutic interventions.

Strict Allergen Avoidance

Avoiding peanuts and tree nuts requires careful attention to food labels, understanding manufacturing practices, and awareness of hidden sources. Food manufacturers are required to clearly label major allergens including peanuts and tree nuts. However, precautionary advisory labels (such as "may contain traces of peanuts") are voluntary and inconsistent across manufacturers. Learning to read ingredient lists thoroughly, asking about ingredients when dining out, and being cautious with unlabeled foods are essential skills for managing these allergies.

Emergency Medications

All individuals with peanut or tree nut allergy should have access to emergency medications and an anaphylaxis action plan. This typically includes:

• Epinephrine auto-injectors: At least two auto-injectors (EpiPen, Jext, Auvi-Q, or generic) should be carried at all times. Epinephrine is the first-line treatment for anaphylaxis and should be used immediately at the first signs of a severe reaction.
• Antihistamines: Non-sedating antihistamines (like cetirizine or loratadine) can help with mild symptoms like hives and itching but are not a substitute for epinephrine in severe reactions.
• Corticosteroids: Sometimes prescribed to reduce prolonged allergic inflammation, though they work too slowly to treat acute anaphylaxis.
• Bronchodilators: For patients with asthma who may experience breathing difficulties.

Oral Immunotherapy (OIT)

Oral immunotherapy involves consuming gradually increasing amounts of the allergenic food under medical supervision to increase tolerance. The FDA-approved peanut oral immunotherapy product (Palforzia) is available for patients aged 4-17 years with confirmed peanut allergy. OIT can increase the threshold amount of peanut that can be tolerated before a reaction occurs, potentially providing protection against accidental exposures. However, OIT does not cure peanut allergy, requires ongoing daily dosing to maintain tolerance, and can cause allergic reactions during treatment. The decision to pursue OIT should be made in consultation with an experienced allergist.

Can Peanut Allergy Be Prevented?

Research shows that early introduction of peanuts (around 4-6 months of age) in high-risk infants can reduce peanut allergy development by up to 80%. The LEAP study demonstrated this breakthrough finding. Peanut products should be introduced as smooth peanut butter or puffed snacks, not whole peanuts, and continued regularly.

The prevention of peanut allergy has been revolutionized by landmark research published in the past decade. Previously, guidelines recommended delaying peanut introduction in high-risk infants, but this approach may have actually contributed to rising peanut allergy rates. Current evidence strongly supports early introduction as a prevention strategy.

The LEAP Study

The Learning Early About Peanut Allergy (LEAP) study, published in the New England Journal of Medicine in 2015, was a groundbreaking randomized controlled trial. It enrolled 640 infants aged 4-11 months who were considered high risk for peanut allergy (having severe eczema, egg allergy, or both). Infants were randomly assigned to either consume peanut-containing foods regularly or avoid peanuts until age 5 years. The results were striking: early peanut introduction reduced peanut allergy development by approximately 81% compared to avoidance.

Current Prevention Guidelines

Based on LEAP and subsequent studies, major allergy organizations now recommend early peanut introduction for high-risk infants. The approach depends on the infant's risk level:

• High-risk infants (severe eczema and/or egg allergy): Should undergo allergy evaluation before introduction. If testing is negative or mildly positive, introduction should occur around 4-6 months under medical guidance.
• Moderate-risk infants (mild to moderate eczema): Can generally begin peanut-containing foods around 6 months of age, at home.
• Low-risk infants (no eczema or food allergies): Can be introduced to peanut-containing foods freely along with other solid foods.

Once introduced, peanut consumption should continue regularly (approximately 2-3 times per week) to maintain tolerance. Stopping consumption may allow allergy to develop. Peanut products for infants should be age-appropriate - smooth peanut butter thinned with breast milk, formula, or pureed fruit, or puffed peanut snacks that dissolve easily. Whole peanuts are a choking hazard and should never be given to young children.

How Can I Manage Living with Peanut or Tree Nut Allergy?

Managing nut allergies requires vigilant label reading, communicating about your allergy when dining out, educating family and caregivers, and always carrying emergency medications. Creating a written allergy action plan and wearing medical identification can be lifesaving in emergencies.

Living with peanut or tree nut allergy involves developing skills and strategies for safe navigation of daily life. While these allergies require constant vigilance, with proper education and preparation, individuals with nut allergies can live full, active lives.

Reading Food Labels

Careful label reading is fundamental to allergen avoidance. In many countries, food manufacturers are legally required to declare peanuts and tree nuts as ingredients. However, it's important to read labels every time you purchase a product, as formulations can change. Be aware that peanuts and tree nuts can be found in unexpected products including cereals and granola, baked goods and chocolate, Asian and African cuisines, sauces and dressings, ice cream and desserts, cosmetics and personal care products, and pet foods.

Dining Out Safely

Eating outside the home requires careful communication. When dining at restaurants, inform the staff about your allergy, ask about ingredients and preparation methods, inquire whether the kitchen can accommodate allergen-free preparation, and be cautious with cuisines that commonly use nuts (Thai, Chinese, Indian, Mediterranean). Consider carrying a chef card that clearly explains your allergy in relevant languages when traveling.

School and Work Accommodations

Schools and workplaces should have protocols for managing food allergies. For children, this includes providing a written allergy action plan to the school, ensuring emergency medications are accessible, training staff on recognizing and responding to reactions, establishing nut-free zones or policies as appropriate, and teaching the child to self-advocate and avoid sharing food. Adults should inform coworkers and supervisors about their allergy and keep emergency medications at work.

Medical Identification

Wearing medical identification jewelry (bracelet or necklace) that clearly states your allergy can be crucial in emergencies when you may be unable to communicate. This ensures first responders and medical personnel are immediately aware of your condition.

Related Allergies and Cross-Reactivity

People with peanut allergy may cross-react with other legumes (5-10%) or tree nuts (25-40%). Tree nut allergies often involve multiple nuts. Birch pollen allergy can cause oral allergy syndrome with nuts. Your allergist can determine which foods you need to avoid through comprehensive testing.

Understanding cross-reactivity patterns is important for comprehensive allergy management. While having one food allergy increases the risk of having others, most people don't need to avoid all potentially cross-reactive foods unless specifically advised by their allergist based on testing and clinical history.

Peanut and Legume Cross-Reactivity

Although peanuts are legumes, most people with peanut allergy (approximately 90-95%) can safely consume other legumes including beans, lentils, peas, and chickpeas. However, some individuals may react to specific legumes. Lupine (lupin), a legume increasingly used in European baking, has significant cross-reactivity with peanut and should be avoided by those with peanut allergy. Soy is generally safe for most peanut-allergic individuals, though testing may be recommended for those with concerns.

Tree Nut Cross-Reactivity

Cross-reactivity among tree nuts is more common than between peanuts and tree nuts. Certain tree nuts tend to cross-react more frequently: walnut and pecan (both are Juglandaceae family), cashew and pistachio (both are Anacardiaceae family), and almond is more distantly related and may be tolerated by some tree nut allergic individuals. Many allergists previously recommended avoiding all tree nuts if allergic to one, but more personalized approaches based on component testing and oral challenges are becoming common.