Allergies

An allergy is a mistake of recognition. The immune system takes a harmless protein — a fragment of nut, cat saliva, wasp venom — for a danger and mounts against it a defence designed for parasites. What harms you is not the nut but the reaction to it. The range is wide: from an itchy nose in May to a situation counted in minutes. This page is about allergy as a whole: how it works, what the dangerous form looks like and what to do about it.

Why the body gets it wrong

At the first meeting with a substance the immune system makes antibodies against it and settles them on the mast cells of the skin, the linings and the gut. That first meeting passes unnoticed. At the next one those cells recognise the familiar protein and release their stores in one burst, histamine above all: vessels start to leak, tissues swell, smooth muscle tightens and the skin itches.

Hence a consequence that throws many people off: "I have eaten it a hundred times and nothing happened" proves nothing. Allergy to a food you have known for years can appear at any age. The reverse holds too: childhood allergy to milk and egg fades in most children before school, while allergy to peanut, tree nuts, fish and shellfish more often stays for life.

The risk is higher when allergy, asthma or eczema runs in close family. What is inherited is not a particular allergen but the tendency to react.

What sets a reaction off most often

• Breathed in: tree and grass pollen, house dust mite, mould spores, proteins from cats, dogs, rodents and horses.
• Food: peanut, tree nuts, milk, egg, fish, molluscs and crustaceans, wheat, soya, sesame.
• Insect venom: stings from bees, wasps and hornets.
• Medicines: most often antibiotics of the penicillin group and non-steroidal anti-inflammatory drugs.
• Contact: latex, nickel in jewellery, dyes and cosmetic preservatives.

Amplifiers deserve a mention of their own. The same portion of food can pass without trouble, or produce a severe reaction if shortly before or after there was physical exertion, alcohol, a painkiller from the non-steroidal anti-inflammatory group, a short night or an infection. So "it was mild last time" is no guarantee for the next.

What a reaction looks like

Symptoms usually appear in the first minutes, and in food allergy within two hours.

• skin: itching, weals like a nettle sting, swelling of eyelids, lips and ears;
• nose and eyes: sneezing, watery discharge, soreness and tears;
• abdomen: nausea, vomiting, cramps, diarrhoea;
• breathing: cough, wheeze, hoarseness, a lump in the throat;
• general state: sudden weakness, pallor, cold sweat.

The key distinction is simple. If only the skin or only the nose is involved, the reaction is mild. If two systems or more are hit at once, above all breathing or circulation, it is anaphylaxis and must be handled as such.

Anaphylaxis: the first minutes

Call an ambulance immediately (112 across Europe) if the person:

• has swollen lips, tongue or throat, a changed voice or trouble swallowing;
• is breathless, wheezing, coughing without a break or feels they are choking;
• turns pale, grey or blue; on darker skin this shows better on the palms, soles and lips;
• becomes suddenly dizzy or confused, sags or loses consciousness;
• is a child who has gone floppy, cannot hold their head up or does not respond as usual.

What to do while help is on the way:

• Give adrenaline with the auto-injector if one is available, into the outer thigh, through clothing if need be. Delay is more dangerous than an unnecessary injection. Antihistamine tablets and an asthma inhaler are no substitute for adrenaline.
• Lay the person down. Raise the legs and do not let them sit up or stand suddenly: with the blood pressure falling, that alone is dangerous. If breathing is hard, half-sitting; if unconscious but breathing, on their side; if pregnant, on the left side.
• Note the time of the injection. If there is no improvement after 5 to 10 minutes, a second dose is given where one is available.
• Go to hospital even if things have improved. A second wave can arrive some hours later without any fresh contact with the allergen.

Allergy, intolerance and coincidence

Not everything that disagrees with you is an allergy, and the confusion is expensive.

Intolerance — to lactose, for example — is a missing enzyme. The immune system plays no part and the reaction depends on the amount: a spoonful of milk in coffee passes unnoticed, a glass brings bloating and diarrhoea. It does not threaten life.

Coeliac disease is an immune condition but not an allergy: there the reaction to gluten damages the gut lining gradually and is diagnosed in other ways.

Allergy can be triggered by traces, and severity cannot be predicted from what happened last time.

The same heading covers poisoning from stale fish and reactions to chilli or to sulphites in wine: they look similar from the outside but are built differently.

How the cause is tracked down

The main tool is a detailed account: what you ate or breathed, how much, how many minutes before it started, what else happened that day and how it ended. Tests only confirm the theory that grows out of that account.

Skin prick tests are used, along with blood tests for specific antibodies, patch tests in contact dermatitis and, when food allergy is unclear, a supervised challenge carried out where there are means to treat a reaction.

One important subtlety: a positive test without a matching history means sensitisation, not disease. That is why testing "for everything at once" does harm: it throws up findings that keep people avoiding foods they eat quite happily for years.

And separately, what is not worth paying for. Food IgG antibody panels, hair analysis, bioresonance and kinesiology do not detect allergy. Their output is an arbitrary list of foods, followed by unjustified diets and, in children, nutritional gaps.

What helps you live an ordinary life

• Know your allergen precisely and read labels: in the European Union the main food allergens must be highlighted in the ingredient list.
• In a restaurant or at someone's home, do not just say "I am allergic" — name the substance and say the reaction can be severe.
• Keep an antihistamine to hand for mild reactions and, where severe ones are possible, two auto-injectors; watch the expiry date and know how to use them.
• Teach family, school or colleagues: during a reaction the person often can no longer help themselves.
• Keep asthma under control, because poorly controlled asthma makes food reactions markedly worse.
• Wear a bracelet or carry a card naming the allergen.
• Discuss immunotherapy with an allergy specialist: for pollen, mites and insect venom it lowers the severity of reactions for a long time.

Online consultation

A remote appointment earns its place exactly where going through the history decides everything. The doctor will rebuild the episode minute by minute, help separate allergy from intolerance, explain which investigations are justified and which are money wasted, and go over your action plan for a reaction and the handling of an auto-injector. If a reaction is already unfolding, a consultation is not what you need — the emergency number is.

This material is for information only and does not replace medical advice.