Food allergies are undoubtedly becoming more and more common. They are considered the second wave of allergies, after respiratory allergies, which have now reached a plateau. It is estimated that 3 to 6% of adults and 6 to 8% of children are affected*.
Most common allergens
Food allergies always involve proteins, whether from animals or plants. They are mainly those contained in the following 14 foods:
- tree nuts
- gluten-containing cereals
- sesame seeds
The list of major allergens is revised periodically, according to the most recent scientific findings. It should be noted that traces of these foods may be sufficient to trigger an allergic reaction.
How food allergies work
The immune system enables the body to defend itself (e.g. against a virus) by producing antibodies (immunoglobulins or Ig).
When a food allergy occurs, the body identifies as dangerous a plant or animal protein that is in reality harmless. In response to this perceived danger, it triggers a defence reaction mediated by the immune system’s immunoglobulin E (IgE), which attacks the allergens involved.
More specifically, a food allergy occurs in two stages:
– the body comes into contact with the allergen for the first time, but no symptoms appear. However, it is sensitized to the food in question and produces antibodies to fight it (especially immunoglobulin E). Hence the expression “food sensitization”. These antibodies bind to cells involved in the immune defence, known as mast cells.
– a new ingestion of the allergen stimulates the mast cells, which then release substances such as histamine, responsible for the onset of symptoms.
Symptoms and risks associated with a food allergy
The symptoms, which can be manyfold, are caused by the body’s defensive reaction. Their nature and intensity vary from one person to another.
Symptoms generally appear within a few minutes to two hours after the allergens have been ingested. Whether they are immediate or delayed, they may occur alone or in combination and include the following:
- skin symptoms: skin pruritus, hives, angioedema;
- respiratory symptoms: rhinitis, dyspnea (difficulty breathing), cough, stridor (high-pitched noise when inhaling);
- digestive symptoms: abdominal cramping, diarrhea, nausea, vomiting; and
- cardiovascular symptoms: hypotension, dizziness, loss of consciousness.
Symptoms can go as far as anaphylactic shock, which is the strongest allergic reaction and may lead to death. An anaphylactic reaction is particular in that it affects the entire body, including the cardiovascular, neurological, respiratory, skin and mucous membrane systems. It requires emergency treatment (intramuscular injection of adrenaline). Food allergies are the main cause of severe anaphylactic reactions in Europe.
How to handle an allergy
The only way to deal with a food allergy is to remove the foods involved, including any trace amounts of them. This requires great caution, especially when it comes to industrial foods, the labels of which must be read very carefully.
* This article covers type I (so-called immediate, IgE-mediated) food allergies. There are other types of food allergies (like the so-called delayed allergies, mediated by IgG, which will be the subject of further articles).
Main sources: Revue Médicale Suisse, 2014 ; 10 : 846-53. Allergie ou intolérance alimentaire ?
Revue Médicale Suisse, 2016 ; 12 : 677-82. Allergies alimentaires de l’enfant : un défi diagnostique.