A food allergy is an IgE-mediated immune response (or non-IgE-mediated in some forms) to specific food proteins. It's not a food intolerance (different mechanism, less immediate consequences): your immune system mistakes a harmless food protein for a threat and triggers a disproportionate defensive response. It affects 3–4% of adults and 6–8% of children in Europe, with an increasing trend over recent decades in high-income countries.

The immunological mechanism: why allergies develop

On first exposure to an allergen, the immune system produces specific IgE antibodies that bind to mast cells (found in mucous membranes) and basophils (in the blood). This phase is called sensitization: no symptoms occur. On second exposure (or later), the IgE antibodies recognize the allergen and activate mast cells, which release histamine, prostaglandins, and leukotrienes. The allergic response appears within minutes: hives, swelling, breathing difficulty, drop in blood pressure.

Why does the immune system "make a mistake" this way? The hygiene hypothesis (now more precisely called the "old friends hypothesis") suggests that children's immune systems in developed countries, not exposed enough to microbes and parasites during development (due to excessive hygiene, antibiotics, limited outdoor time), become "bored" and reactive to harmless stimuli like food proteins. This would explain the rise in allergies over the past 50 years in high-income countries.

Symptoms and severity levels

Symptoms range from localized hives to potentially fatal anaphylaxis. Mild to moderate symptoms: itching, hives, angioedema (swelling of lips, eyes, throat), rhinitis, conjunctivitis, abdominal pain, nausea, vomiting. Severe symptoms (anaphylaxis): acute breathing difficulty, laryngeal stridor, drop in blood pressure, loss of consciousness. Anaphylaxis is a medical emergency: it requires injectable epinephrine (EpiPen) and an immediate call to emergency services. The reaction time is minutes: carrying an auto-injectable epinephrine pen is literally lifesaving for anyone with a history of severe reactions.

The 14 major allergens: European legal requirement

EU Regulation 1169/2011 mandates the declaration of 14 allergens on labels: cereals containing gluten, crustaceans, eggs, fish, peanuts, soy, milk, tree nuts (almonds, hazelnuts, walnuts, cashews, pecans, pistachios, Brazil nuts, macadamia), celery, mustard, sesame seeds, sulfur dioxide and sulfites, lupin, mollusks. Note: this list is based on the most common allergies in Europe. Allergies to many other foods exist (kiwi, peaches, strawberries, corn) that are not on this mandatory list.

Allergy vs. intolerance: critical differences

Food allergy: immune-mediated, rapid response (minutes), potentially fatal even in tiny amounts, requires complete elimination of the allergen for life. Food intolerance: not immune-mediated (enzymatic deficiency, pharmacological mechanism), dose-dependent response (small amounts often tolerated), never fatal, managed by reducing quantity or enzymatic supplementation. Confusing them can be dangerous: someone who thinks they have "just a peanut intolerance" and eats them in reduced amounts risks anaphylaxis.

Diagnosis: how to do it correctly

Diagnosing a food allergy requires: detailed clinical history (when, what, how much, what symptoms), skin tests (prick test) with standardized extracts of suspected allergens, specific IgE blood testing (RAST or ImmunoCAP). Definitive diagnostic confirmation in many cases requires a controlled oral provocation test (OFC) in a medical setting: the patient consumes increasing amounts of the suspected food under medical supervision with emergency equipment available. Never self-diagnose: many people eliminate foods without true allergy, unnecessarily reducing quality of life.

Managing daily life with a severe food allergy

Always carry your auto-injectable epinephrine if you've had severe reactions. Wear a medical alert bracelet with your allergy information. Always inform restaurants with specifics (not "I'm allergic to peanuts" but "I have a severe peanut allergy—even traces can cause anaphylaxis. Can I eat this dish?"). Always read labels, even on products you know: formulas change. Inform friends, family, and colleagues of your emergency plan.

Oral immunotherapy (OIT): the therapeutic frontier

Oral immunotherapy (OIT) is a medical procedure that in many cases allows you to increase your tolerance threshold to an allergen, reducing the risk of accidental reaction. It's performed in specialized centers: the patient takes increasing amounts of the allergen in a controlled setting over months. It's not a permanent cure and isn't suitable for everyone, but it has transformed the lives of many people with severe allergies to milk, eggs, and peanuts. Ask an allergist if you're a candidate.

Nickel allergy: the most common and least known

Nickel allergy isn't among the 14 mandatory allergens but affects 10–15% of women in Europe. Nickel is present in many foods: whole grains, legumes, nuts, cocoa, tomatoes, spinach. It manifests mainly as contact dermatitis (earrings, buckles) but in severe forms causes eczema and gastrointestinal symptoms. If you suspect nickel allergy: consult a dermatological allergist for patch testing. A low-nickel diet is complex: it requires specialist supervision.

Build your list of safe substitutes

For each food you're allergic to, identify at least three nutritionally equivalent alternatives with a dietitian specializing in food allergies. Milk allergy: fortified soy milk (similar protein and calcium), fortified oat milk, calcium-set tofu. Egg allergy: ground flaxseed in water (for baking), aquafaba (chickpea water for egg whites in recipes). Wheat allergy: brown rice, quinoa, corn, buckwheat. A written list is the most practical tool for not losing key nutrients when eliminating a food.