Peanut Allergy

In botanical terms, the peanut is not a nut, but a legume. It is one of the types of food that often provoke severe allergic reactions. In some cases, trace amounts of one milligram can trigger a reaction. In comparison, a peanut weighs between 500 and 1000 milligrams.

Around one to two per cent of all children in industrialised countries are allergic to peanuts. When considering only those studies in which a peanut allergy was confirmed through a provocation test, it has been demonstrated that 0.2 per cent of the entire European population is allergic to peanuts.

Triggers

The most common form is the primary food allergy, which most frequently appears in childhood. Allergic individuals react to certain proteins in the peanut, usually storage proteins. These proteins are important for the growth of the plant and are so stable that they cannot be altered by heat or stomach acid. If test results reveal a high level of IgE antibodies against the storage protein Ara h 2 in the blood, there is often a high risk of severe allergic reactions.

In Europe and the U.S., peanuts are often consumed roasted – in the shell, shelled, or processed into peanut butter and peanut puffs. In Asia, the legumes are usually used raw in cooking. Whether raw, roasted or cooked, peanuts in any form can provoke allergic reactions. In fact, roasting processes appear to increase allergenicity, while cooking raw peanuts for a longer time appears to lower allergenicity. Peanut oil can also trigger allergy symptoms. Refined (heat-processed) peanut oil is usually better tolerated than cold-pressed peanut oil.

In accordance with European food regulations, all foods containing peanuts must be labelled as such. This information must also be provided for non-packaged foods. Products that do not contain peanuts can still have traces of the legumes if peanuts are processed in the same production facility. It is not always possible to tell whether this is the case because the warning ‘may contain traces of peanuts’ is not mandatory for the manufacturer. However, a 2015 study from the Federal Institute for Risk Assessment (BfR) revealed that most manufacturers do follow the recommendation. Out of 633 products (including breakfast cereals, pizzas and sweets) that did not carry the warning, only two samples contained very small traces of peanuts. Individuals with a severe allergy can ensure greater safety by contacting manufacturers directly.

Symptoms

A peanut allergy can cause mild or severe reactions in various organs. Symptoms range from what is called oral allergy syndrome, in which the mucosa in the mouth and throat start to tingle or swell a few minutes to hours after exposure, to anaphylactic shock accompanied by difficulty breathing and circulatory collapse.

It can lead to abdominal pain, vomiting or diarrhoea. In some cases, the airways are affected and allergic rhinitis or asthma symptoms can develop. The skin may also develop allergic reactions. Apart from itchiness, redness and hives, a peanut allergy can also trigger or worsen an eczema flare-up. In particular, adolescents and young adults with bronchial asthma are among those at risk of suffering from severe anaphylactic reactions.

Peanut Allergy in Childhood

Peanut allergies usually appear in childhood and remain for life in around 80 per cent of allergic individuals. Since peanuts are a ‘hidden’ allergen in many food products and can provoke life-threatening reactions, proper diagnosis is important. When a child is highly allergic to peanuts, it often has a big impact on the quality of life for the whole family. Any food outside the home – at kindergarten, at school or in other people’s homes – can become a problem. Nutritional counselling and anaphylaxis training are recommended for children and parents in order to handle the risks that may be encountered in everyday life. 

Peanut Allergy in Adulthood

Peanut allergies that appear for the first time in adolescents or adults are usually secondary allergies. These individuals may have initially been allergic to birch pollen (or grass pollen). Since some proteins in these plants are structurally similar to certain peanut proteins, a peanut allergy can also develop through what is known as cross-reactivity. Secondary peanut allergies are usually milder and the reactions are limited to the mouth and throat area.

Diagnostic Procedure

As a first step in diagnosing a peanut allergy, the doctor asks the patient about his or her eating habits and symptoms. If an allergy is suspected, skin and/or blood tests are conducted in order to confirm it. These tests reveal an allergic disposition to certain substances but do not provide evidence of an actual allergy. One in ten children in Germany have peanut-specific IgE antibodies in the blood. However, only a fraction of them suffer from an allergy. For this reason, an additional diagnostic procedure, the provocation test, is conducted to rule out any doubts. For this test, the patient is given the smallest traces of an allergen under medical supervision. The results reveal whether the peanut triggers an allergic reaction (and if so, in which amount) or whether it can be removed from the list of suspected allergens. 

Therapy

Allergen avoidance is the most effective treatment for peanut allergies.

People who are highly allergic to peanuts and at risk of anaphylactic shock from exposure to the smallest trace of peanut protein must carry an emergency kit with them containing an adrenaline auto-injector, a corticosteroid (in liquid or tablet form) and an antihistamine (in liquid or tablet form).

Immunotherapy (hyposensitisation), which is used to treat pollen, insect venom and house dust mite allergies, cannot be applied to food allergies. However, studies from 2014 suggest that hyposensitisation may be effectively used to treat peanut allergies in the future. This involves giving the patient small doses of peanut protein and stimulating the immune system by building up to increasingly larger amounts, which can then be tolerated by the end of the therapy. However, the side effects and the length of efficacy need to be further investigated. Until we know more, this therapy should not be used outside of clinical studies due to the potentially serious adverse effects.

Legal notes

Prof. Dr. med. Dr. h.c. T. Zuberbier
Last changes made: July 2016