What is a food allergy?
Your immune system is the body's guard. It fights germs. In a food allergy the guard makes a mistake and fights a harmless food protein. The protein that causes this is called an allergen.
Allergy is not the same as food intolerance. In intolerance the immune system is not involved. For example, some people cannot digest milk sugar (lactose), so they get a stomach ache. It is unpleasant but not usually dangerous. An allergy can be life-threatening even with a tiny amount.
How the body reacts
- First exposure (sensitisation): the body makes IgE antibodies against the allergen. They stick on mast cells. No symptoms yet.
- Next exposure: the allergen joins the antibodies. The mast cells release histamine.
- Symptoms start, often within minutes to two hours.
Mild signs: itchy mouth, hives (red itchy bumps), runny nose, stomach pain, vomiting. Serious signs: swollen lips or throat, wheezing, dizziness, fainting. A severe whole-body reaction is called anaphylaxis. It needs emergency help at once.
Common allergens
Most reactions come from a few foods: milk, egg, peanut, tree nuts, wheat, soy, fish, shellfish and sesame. Different countries list slightly different foods that must be shown on labels, but the idea is the same. Some children outgrow milk or egg allergy; peanut, nut and shellfish allergies often last for life.
Allergens can hide in sauces, bakery items, sweets and ready meals. Cooking usually does not remove them.
Prevention and safe eating
- Get a diagnosis. A doctor finds the exact allergen with history, skin test or blood test. Do not guess and cut out many foods without advice.
- Read every label. Look for the allergen in the ingredient list and in 'may contain' warnings. Read again each time, because recipes change.
- Avoid cross-contact. Use clean knives, boards and pans. Wash hands with soap. Water alone is not enough on dirty utensils.
- Tell others. School, cooks and friends must know. Wear or carry an allergy card.
- Eating out: ask what is in the dish and how it was made.
- Be ready. Keep the medicine the doctor prescribed (such as antihistamine or an adrenaline auto-injector) with you. Know how to use it and call emergency help after using it.
- Babies: current advice from many health bodies is to introduce common allergens like peanut and egg early in a safe form, but only as your doctor advises, especially if the baby has eczema.
Food hygiene and allergy together
Food businesses must keep allergen foods separate, clean equipment between batches and show allergens on the pack. This is part of food safety law in many countries. A clean kitchen stops germs; an allergen plan stops allergic reactions. They are different problems and both need care.
Try it
In the 3D, choose 'milk' as the allergy. Predict first: how many foods must be avoided? Then check. Now pick 'wheat'. At home, read the labels of three packed foods and underline any of the nine common allergens you find.
Key formulas and definitions
- Allergen = the harmless food protein that triggers the reaction
- Allergy = immune system reaction (IgE + mast cells + histamine)
- Intolerance = digestion problem, immune system not involved
- Anaphylaxis = severe, whole-body reaction: call emergency help at once
- Prevention = know it, read it, keep it apart, tell people, be ready
Worked examples
1. A child gets hives and a swollen lip five minutes after eating a biscuit. Allergy or intolerance?
Hives and swelling come fast and involve the immune system, so it is likely an allergy. The child needs medical help, and the biscuit label should be checked for allergens.
2. A man gets a bloated tummy after drinking milk but has no rash or breathing trouble. What may it be?
Most likely lactose intolerance: the gut cannot digest milk sugar. The immune system is not involved, so it is not a true milk allergy. A doctor can confirm.
3. A school cook has to make a sandwich for a child with a peanut allergy. List three safe steps.
Wash hands and use a clean board and knife that never touched peanut. Check the bread and spread labels for peanut or 'may contain peanut'. Keep the sandwich covered and apart from other food.
4. Why is it unsafe to just pick the peanut out of a cake and eat the rest?
Peanut protein spreads into the cake as crumbs, oil and dust. Even a trace can start a reaction. Taking the nut out does not make the cake safe.
Common mistakes
- Thinking a small amount is always safe. For some people a tiny trace is enough.
- Mixing up allergy and intolerance. Allergy involves the immune system and can be life-threatening.
- Reading the label only once. Makers change recipes, so read it every time.
- Believing cooking or washing the food removes the allergen. Cooking usually does not.