What to do in case of a food allergy on the skin?

The very first instinct in the event of a food allergy is to assess the severity of the reaction. In most cases, this is limited to a skin rash of the urticaria type, characterised by raised, itchy red patches. However, it can happen that the swelling of the skin affects the larynx or pharynx, leading to a major respiratory discomfort. This type of food allergy represents an absolute medical emergency, due to the accompanying risk of choking. Another danger found in certain food allergies is anaphylaxis, a severe, potentially fatal allergic reaction. It manifests as breathing difficulties, swelling of the face or throat, nausea, vomiting, a drop in blood pressure, and dizziness.

In the event of an allergic angioedema with anaphylactic shock, it is crucial to immediately call for emergency assistance by dialling 15 for the SAMU in France, 911 in the United States, 999 in the United Kingdom, or 116 117 in Germany.

While waiting for help, if the person affected by the food allergy carries with them a dose of injectable adrenaline, often presented in the form of an auto-injector pen, that is, an epipen, it must be urgently administered to them. If there is no response within the following five to ten minutes, a new dose can be injected. Adrenaline typically acts within a few minutes to reduce vasodilation, increase blood pressure, and decrease swelling. The patient should then be transported to the hospital, where they will receive further care.

Some allergic reactions can be quite striking and affect the entire body.

If the food allergy only affects the skin and does not appear to pose a risk of anaphylactic shock, it is not necessary to alert emergency services. However, it is advisable to consult a doctor promptly to ensure this and receive appropriate treatment. Most often, antihistamines are prescribed to reduce allergic symptoms. As their name suggests, these medications work by blocking the specific receptors of histamine, thus preventing the attachment of this mediator and the cascade of inflammatory reactions it triggers.

In cases where antihistamines are ineffective and the allergic skin reaction persists, a doctor may prescribe dermocorticoids, such as hydrocortisone or betamethasone. These creams reduce local inflammation by inhibiting the release of pro-inflammatory cytokines and reducing the activity of the transcription factor NF-κB through the activation of the IkB gene transcription, thereby helping to alleviate inflammatory symptoms. However, corticoids should not be used over a prolonged period as they can lead to thinning and weakening of the skin.

Once the reaction has been managed, it is crucial to ensure that it does not recur in the future by proceeding with the elimination of the responsible food allergen. To do this, it must first be identified, which can be done during an allergy assessment carried out by an allergist. Most often, a prick test is performed. This test involves placing a drop of several allergens on the skin, before lightly pricking it to allow the substances to penetrate the epidermis. In the event of an allergy, swelling, redness or itching appear within a few minutes at the injection point of the allergen.

If the prick test does not yield results, the allergist may perform a specific IgE assay, which involves a blood test. To be considered normal, the total IgE level in the blood should be less than 150 IU/ml (International Units per millilitre). Beyond this value, an allergy is suspected.

The identification of the responsible food allergen must absolutely be carried out with an allergist and not independently at home, in order to avoid a new allergic reaction, which could potentially be severe.

Once the allergen is identified, it is essential to adapt one's diet to prevent recurrences. This involves completely eliminating the offending food and carefully reading the labels of food products to spot potentially hidden allergenic ingredients. Terms such as "traces of" or "produced in a factory handling allergens" should not be overlooked and can alert to the potential allergenicity of a food.

Informing your close ones is also a good practice to adopt when suffering from food allergies, especially if they often invite you for lunch or dinner. In addition, it is beneficial for them to recognise the signs of a severe allergic reaction, such as anaphylaxis. Explaining to your acquaintances how to use an adrenaline auto-injector pen can also make a difference in an emergency situation.

Note : Just because your child suffers from a food allergy, it doesn't mean they can't have lunch at the school canteen. If you wish to enrol them, you simply need to establish an Individualised Welcome Plan (IWP) with their school.

• WERFEL T. Skin manifestations in food allergy. European Journal of Allergy and Clinical Immunology (2004).

• PUCCI S. & al. Allergy and the skin. Clinical and Experimental Immunology (2008).

• WATSON W. & al. Food allergy. Allergy, Asthma & Clinical Immunology (2011).

• SIMON D. & al. Update on skin allergy. European Journal of Allergy and Clinical Immunology (2014).