A food allergy is an immune reaction to a food protein. It differs fundamentally from food intolerance: an allergy involves the immune system and can be life-threatening, while an intolerance is a digestive problem that is unpleasant but not dangerous. Confusing the two leads people to underestimate a genuine allergy.
This guide covers the symptoms, how allergy is diagnosed, and — most importantly — what to do in a severe reaction.
Short answer: Food allergy symptoms appear within minutes to two hours and range from hives and swelling to vomiting and breathing difficulty. Anaphylaxis is a medical emergency treated with adrenaline, not antihistamines. If someone has breathing difficulty, throat tightness, or collapses after eating, use an adrenaline auto-injector if available and call emergency services immediately.
Allergy Is Not Intolerance
| Food allergy | Food intolerance | |
|---|---|---|
| Mechanism | Immune system reaction to a protein | Digestive — often a missing enzyme |
| Onset | Minutes to 2 hours | Hours, sometimes longer |
| Amount needed | Trace amounts can trigger it | Usually dose-related |
| Symptoms | Skin, breathing, gut, circulation | Mostly digestive |
| Life-threatening? | Yes | No |
Lactose intolerance, for instance, is an enzyme deficiency causing bloating and diarrhoea. Milk allergy is an immune reaction that can cause anaphylaxis. They are entirely different problems that happen to involve the same food.
Symptoms
Mild to Moderate
- Hives, welts or an itchy rash
- Swelling of the lips, face or eyes
- Tingling or itching in the mouth
- Nausea, vomiting, stomach cramps or diarrhoea
- Runny nose, sneezing, watery eyes
Anaphylaxis — Call Emergency Services
- Difficulty breathing, wheezing, or noisy breathing
- Swelling or tightness of the throat
- Difficulty talking, or a hoarse voice
- Persistent dizziness or collapse
- Pale and floppy, in a young child
- A sudden sense that something is seriously wrong
Anaphylaxis can develop within minutes. It can also occur without any skin symptoms at all, which is why waiting for hives before acting is dangerous.
What to Do in an Emergency
- Use the adrenaline auto-injector immediately — into the outer thigh, through clothing if necessary
- Call emergency services, stating anaphylaxis
- Lie the person flat with legs raised. If breathing is difficult, sitting up is acceptable — do not stand them up or walk them, as this can cause sudden collapse
- Give a second dose after 5 minutes if there is no improvement and a second injector is available
- Go to hospital regardless of recovery — symptoms can return hours later in a biphasic reaction
Antihistamines do not treat anaphylaxis. This is the most dangerous misconception about food allergy. Antihistamines help hives and itching; they do not act on the airway swelling or the drop in blood pressure that make anaphylaxis lethal. Giving an antihistamine instead of adrenaline, or waiting to see whether it works, costs time that matters. Adrenaline is the only first-line treatment.
The Common Culprits
A small number of foods account for the majority of allergies: milk, eggs, peanuts, tree nuts, soy, wheat, fish, shellfish and sesame.
Children frequently outgrow milk, egg, wheat and soy allergies. Peanut, tree nut, fish and shellfish allergies more often persist for life.
Diagnosis
- Clinical history — what was eaten, how quickly symptoms appeared, and what they were. This carries more weight than any single test
- Skin prick testing — a small amount of allergen on the skin
- Specific IgE blood testing — measures antibodies to particular foods
- Supervised oral food challenge — the definitive test, performed only in a medical setting with resuscitation available
A positive test alone does not diagnose allergy. Sensitisation without clinical reaction is common, and acting on test results without a matching history leads to unnecessary food avoidance — which in children can cause nutritional deficiency and, paradoxically, increase the risk of developing true allergy.
Commercial “food intolerance” tests measuring IgG are not validated for diagnosing either allergy or intolerance.
The MedlinePlus food allergy resource covers the diagnostic pathway.
Management
Avoidance and Label Reading
The foundation of management. Learn the alternative names an allergen appears under, and treat “may contain” warnings seriously where the allergy is severe.
Carrying Adrenaline
Anyone prescribed an auto-injector should carry two, kept within temperature range and in date. Everyone around them — family, school, colleagues — should know where they are and how to use them.
Medicines for Milder Symptoms
Antihistamines relieve hives and itching in mild reactions. Non-sedating options include levocetirizine, as Cetcip-L 5 Mg, and loratadine, as Alaspan 10 Mg. Corticosteroids such as methylprednisolone — Medrol 4 Mg — are sometimes prescribed after a reaction, but act too slowly to be useful in an emergency. Related products sit under Allergy.
None of these substitute for adrenaline in anaphylaxis.
Emergency Plan
A written plan naming the allergen, the symptoms to watch for, and the steps to take — shared with schools, workplaces and anyone providing care.
Frequently Asked Questions
What are the symptoms of a food allergy?
Hives, swelling of lips or face, mouth itching, vomiting, cramps and diarrhoea, usually within minutes to two hours. Breathing difficulty, throat tightness or collapse indicate anaphylaxis and are an emergency.
What is the difference between food allergy and intolerance?
Allergy is an immune reaction that can be life-threatening and triggered by traces. Intolerance is a digestive problem, usually dose-related and not dangerous.
Can antihistamines treat anaphylaxis?
No. Antihistamines help hives and itching only. Adrenaline is the only first-line treatment for anaphylaxis, and delay to try an antihistamine is dangerous.
How quickly do reactions start?
Usually within minutes, and almost always within two hours. Anaphylaxis can develop within minutes of exposure.
Can food allergies develop in adulthood?
Yes. Shellfish, fish and tree nut allergies commonly begin in adults, sometimes to foods eaten safely for years.
Can children outgrow food allergies?
Often, with milk, egg, wheat and soy. Peanut, tree nut, fish and shellfish allergies more often persist.
Are home food intolerance tests reliable?
No. IgG-based tests sold direct to consumers are not validated for diagnosing allergy or intolerance and frequently prompt unnecessary food avoidance.
Do I still need hospital care after using adrenaline?
Yes, always. Symptoms can return hours later in a biphasic reaction, so observation is required even after full recovery.
Health and Medical Disclaimer
This article is general information, not medical advice, and does not replace consultation with a qualified healthcare professional or allergy specialist. Anaphylaxis is a medical emergency treated with adrenaline, not antihistamines. If you suspect anaphylaxis, use an adrenaline auto-injector immediately and call emergency services, then attend hospital even if symptoms resolve. Do not attempt to diagnose food allergy through elimination diets or commercial testing without medical supervision, particularly in children, as unnecessary exclusion can cause nutritional deficiency.
