A basic guide to nut allergy

In this basic guide to nut allergy in children and adults, we answer some of the questions patients most frequently ask about this condition.

Allergy to tree nuts and peanuts is among the most important food allergies in childhood and can cause severe reactions, including anaphylaxis. Although peanuts are botanically legumes rather than tree nuts, they are often discussed alongside tree nuts because of their importance in food allergy. Research has shown that early introduction of peanut in selected infants at increased risk of allergy can reduce the likelihood of developing peanut allergy. However, whole nuts present a significant choking hazard in young children, so the way these foods are introduced is particularly important.

Differences between food allergy and food intolerance

It is important to distinguish between food allergy and food intolerance. Although the terms are sometimes used interchangeably, they describe different processes.

A food intolerance does not involve the same immune mechanisms as a food allergy. Symptoms are often gastrointestinal and may include abdominal pain, bloating, gas or diarrhoea. Examples include lactose intolerance, in which the body has difficulty digesting lactose because of reduced lactase activity.

A food allergy, by contrast, involves an abnormal immune response to proteins in a food. Many immediate nut allergies are IgE-mediated, meaning that immunoglobulin E antibodies recognise a food protein as a threat and trigger an allergic reaction after exposure. Symptoms can range from mild to severe and, in some patients, may progress to anaphylaxis.

Symptoms of nut allergy

Symptoms of an IgE-mediated nut allergy usually develop within minutes and generally within two hours of exposure. They can affect the skin, respiratory tract, gastrointestinal system and cardiovascular system. Mild symptoms may include itching or tingling in the mouth, lip swelling or localised hives. More severe reactions can involve several organ systems and may progress to anaphylaxis, which is a medical emergency.

Among the most frequent manifestations are urticaria and angioedema. Urticaria causes raised, itchy wheals on the skin.

Angioedema affects deeper layers of tissue and commonly causes swelling, particularly around areas such as the lips, eyelids or face. It may be accompanied by discomfort, tingling or a feeling of tightness. Swelling affecting the tongue or throat, breathing difficulty, wheezing, marked dizziness or collapse may indicate anaphylaxis and require immediate emergency treatment with adrenaline.

Which nuts cause allergic reactions most frequently?

The most common food allergens vary according to diet and geographical region. Peanut allergy is particularly important in countries such as the United States, while hazelnut allergy is common in parts of Europe.

In Spain, according to research carried out by Dr Elisa Haroun , Head of Grupo Pedro Jaén’s Allergy Unit, walnut is among the tree nuts most frequently associated with allergic reactions, followed by hazelnut and almond, while peanut is also an important cause of food allergy. The individual pattern varies considerably, and being allergic to one nut does not automatically mean that a patient is clinically allergic to all other nuts.

How is nut allergy diagnosed?

Diagnosis begins with a detailed medical history and assessment by a specialist allergist. Depending on the clinical history, testing may include a skin prick test using a standardised allergen extract or, in selected cases, the fresh food itself. A small amount of the allergen is placed on the skin, usually on the forearm, and the skin is gently pricked with a sterile lancet. The reaction is then assessed after approximately 15 minutes. A positive skin test indicates sensitisation, but it does not by itself prove that the patient will develop symptoms when eating the food. For this reason, results must always be interpreted alongside the clinical history.

Further investigation may include a blood test for specific IgE antibodies and, in selected cases, component-resolved diagnostics. When the diagnosis remains uncertain, a supervised oral food challenge may be required. During this test, gradually increasing amounts of the suspected food are administered under close medical supervision.

An oral food challenge can help confirm or rule out a food allergy but must be performed in an appropriate healthcare setting with staff and equipment available to treat an allergic reaction if one occurs. The patient or their parents must receive clear information about the purpose, procedure and potential risks before providing consent.

Treatment of nut allergy in children and adults

The main approach is to avoid the specific nut or nuts that have been confirmed to cause allergic reactions. Patients should learn how to read food labels carefully because nuts may be present as ingredients in processed foods or may be mentioned in precautionary allergen labelling.

Avoiding every nut is not automatically necessary for every patient. The allergist can determine which foods genuinely need to be excluded and whether other nuts can be eaten safely. Patients and families should also understand the emergency treatment plan prescribed by their specialist. Children should gradually be taught how to recognise symptoms and what to do if a reaction occurs when an adult is not immediately available. For patients at risk of anaphylaxis, this generally includes knowing when and how to use an adrenaline auto-injector. Adrenaline is the first-line treatment for anaphylaxis. Antihistamines may help relieve some skin symptoms, while inhaled bronchodilators may be used for associated wheezing, but these treatments do not replace adrenaline when anaphylaxis is suspected.

Schools and other carers should also be informed of a child’s food allergy and have an appropriate written action plan. Staff should know how to reduce the risk of accidental exposure and how to respond in an emergency.

In selected patients, oral immunotherapy may be considered under specialist supervision. The aim is to gradually increase the amount of an allergenic food that the patient can tolerate, thereby reducing the risk of a severe reaction, particularly anaphylaxis, after accidental exposure. The strongest clinical experience is currently with peanut oral immunotherapy, although treatment availability and indications vary. Research and specialist protocols also exist for some tree nut allergies. Oral immunotherapy does not necessarily cure the allergy. Some patients achieve a state of desensitisation, meaning that they can tolerate a larger amount of the allergen while continuing regular exposure according to the prescribed protocol. Treatment must be managed by an experienced allergy team because allergic reactions can occur during therapy.

Prevention of nut allergy

Historically, parents were often advised to delay the introduction of highly allergenic foods. More recent evidence has changed this approach, particularly for peanut allergy. In selected infants at increased risk of allergy — for example, those with severe eczema or an existing food allergy — appropriately timed introduction of peanut during infancy may reduce the risk of developing peanut allergy. Parents of high-risk infants should discuss introduction with their paediatrician or allergist, as some children may require assessment before the food is first given.

Whole nuts must not be given to young children because of the risk of choking. Instead, when age-appropriate and clinically suitable, nuts can be introduced in safe forms such as smooth nut butter, finely ground nuts or nut-containing foods with an appropriate texture.

Can nut allergy disappear with age?

Allergy to peanuts and tree nuts tends to be more persistent than some other childhood food allergies, such as milk or egg allergy. However, it does resolve in a proportion of patients. For this reason, patients should be reassessed periodically when clinically appropriate rather than assuming that the allergy will necessarily persist for life. Any attempt to reintroduce a food that has previously caused an allergic reaction should be guided by an allergist.

If I am allergic to nuts, what other allergies might I have?

Patients with nut allergy may sometimes show cross-reactivity with other foods because different plants can contain structurally similar allergenic proteins. For example, in Mediterranean countries, sensitisation to lipid transfer proteins (LTPs) can be associated with reactions to both nuts and fruits such as peach and other members of the Rosaceae family. This family includes nectarine, apricot, plum, cherry, apple and pear, among others.

However, cross-reactivity identified in allergy testing does not necessarily mean that the patient will have clinical symptoms with every related food. For this reason, when our specialist allergists diagnose a nut allergy, they assess which other plant foods the patient has eaten and tolerated and determine whether any further investigation or avoidance is necessary.

We invite you to share this basic guide to nut allergy in children and adults with family and friends who may find it useful.