Food Allergy or Food Intolerance? They Are Not the Same Thing

“I’m allergic to that” covers two completely different things, and confusing them leads both to unnecessary diets and to dangerous under-preparation for genuine allergy.

The difference

Food allergy is an immune reaction, usually IgE-mediated. It occurs within minutes to two hours, happens with even tiny amounts, is reproducible every time, and can be life-threatening.

Food intolerance is a digestive or metabolic problem with no immune involvement. It is dose-related, so small amounts are often tolerated, comes on more slowly, causes discomfort rather than danger, and varies with circumstances.

Allergy symptoms

• Hives, flushing, swelling of lips, face, eyelids or tongue
• Itching of the mouth and throat
• Vomiting, cramping abdominal pain, diarrhoea
• Runny nose, sneezing, watery eyes
• Cough, wheeze, chest tightness, breathlessness
• Anaphylaxis: throat tightness, difficulty breathing or swallowing, hoarse voice, dizziness, collapse, a sense of impending doom

Intolerance symptoms

Bloating, excess gas, abdominal discomfort, loose stools or constipation, nausea, headaches, and fatigue. Unpleasant, but not dangerous and not anaphylactic.

Lactose intolerance is the classic: deficiency of the lactase enzyme, extremely common in South Asian adults. Most people with it tolerate small amounts, curd and hard cheese better than milk, and lactase tablets.

Non-coeliac gluten sensitivity, FODMAP sensitivity, histamine intolerance and reactions to food additives are other intolerances.

Coeliac disease is a third category: an autoimmune reaction to gluten, neither classic allergy nor simple intolerance, which damages the small intestine and requires lifelong, strict gluten avoidance. It must be tested for before removing gluten from the diet, because the tests become falsely negative once gluten is stopped.

Common food allergens

Milk, egg, peanut, tree nuts, wheat, soy, fish, shellfish and sesame account for most reactions. In Indian practice, milk, egg, peanut, shellfish, sesame and chickpea are frequent.

Many childhood allergies to milk, egg, wheat and soy are outgrown. Peanut, tree nut, fish and shellfish allergies more often persist.

Oral allergy syndrome causes itching of the mouth and lips with raw fruits and vegetables in people allergic to pollen, due to cross-reacting proteins. Cooking usually destroys the protein, so the cooked form is tolerated. It is generally mild.

Testing

Useful tests:

• A careful history, which is the foundation. What was eaten, how much, how long before symptoms, what happened, and whether it recurs
• Skin prick testing
• Specific IgE blood testing
• Component-resolved diagnostics for peanut and some others, which improve accuracy
• Supervised oral food challenge, the definitive test, conducted in a facility equipped for reactions
• A food and symptom diary

Important caveat: a positive skin test or IgE result shows sensitisation, not allergy. Many people have positive tests to foods they eat without any problem. Tests are interpreted alongside history, never alone, and should not be used as a screening panel.

Tests without scientific validity, widely sold and widely misleading:

• IgG or IgG4 food “intolerance” panels. IgG to a food indicates exposure, not intolerance; a positive result to foods you eat regularly is the expected finding
• Hair analysis
• Applied kinesiology and muscle testing
• Electrodermal or Vega testing
• Cytotoxic and leucocyte activation tests
• Pulse testing and iridology

These produce long lists of foods to avoid, lead to unnecessary restriction and nutritional harm, and are especially damaging in children.

Managing genuine allergy

• Strict avoidance of the confirmed allergen
• Read every label, every time; recipes and manufacturers change
• Understand “may contain” warnings and cross-contamination in kitchens
• Tell restaurants clearly, naming the allergen rather than saying “I don’t eat it”
• Carry an adrenaline auto-injector if prescribed, and keep it in date
• Wear or carry medical identification
• Make sure school and workplace have a written emergency plan
• Antihistamines treat mild reactions only. They do not treat anaphylaxis

Anaphylaxis action

1. Give adrenaline immediately into the outer thigh. Do not wait to see if it worsens. Delay is the main factor in deaths
2. Call emergency services
3. Lie the person flat with legs raised. If breathing is difficult, sitting up is acceptable. Do not stand them up or walk them
4. A second dose may be given after 5 to 15 minutes if there is no improvement
5. Go to hospital even if symptoms settle, because a delayed second-phase reaction can occur hours later

Prevention in infants

Current evidence supports early introduction of allergenic foods, including peanut and egg, from around six months alongside other solids, rather than delaying them. Delaying introduction increases the risk of allergy. Infants with severe eczema or existing egg allergy should have this discussed with a doctor first.

This is general information. Do not eliminate major foods, especially from a child’s diet, without proper assessment, and do not rely on unvalidated sensitivity panels.