Food allergies: symptoms, tests, treatment and what to do in a reaction

The NHS says symptoms can affect any part of the body, including different parts at the same time. Allergy UK groups them by body system and says they typically occur within minutes to a couple of hours of eating or coming into contact with the allergen, with severity varying between people.

Because symptoms differ, the same food can cause only an itchy mouth in one person and a life-threatening reaction in another. Never assume that a past mild reaction predicts the next one.

The NHS says that if you have a food allergy you will not be able to eat the food you are allergic to, including foods that contain it as an ingredient. You will be given medicines to manage symptoms or use in an emergency: antihistamines for mild allergic reactions, and adrenaline auto-injectors (such as an EpiPen) or a nasal spray (EURneffy) for severe reactions. Your specialist will give you an allergy action plan.

Allergy UK says the best way to prevent a reaction is to identify the food and avoid it, that antihistamines can relieve mild or moderate symptoms, and that adrenaline is the effective treatment for severe symptoms such as anaphylaxis. The NHS notes that children with a peanut allergy may have immunotherapy to help their bodies become less sensitive, but they should still avoid eating peanuts.

Both sources warn against making radical changes to a diet without advice. The NHS says not to cut foods out without speaking to a GP, and Allergy UK says that for some foods, such as milk, you may need to speak to a dietitian first.

The NHS describes anaphylaxis as a life-threatening allergic reaction that happens very quickly, usually starting within minutes. It says to call 999 if you think you or someone else is having an anaphylactic reaction.

The steps the NHS gives are: use an adrenaline auto-injector if you have one; call 999 for an ambulance and say you think it is anaphylaxis; lie down and raise your legs (or sit up slowly if struggling to breathe, or lie on your left side if pregnant); if there is no improvement after 5 minutes, use a second auto-injector; and do not stand or walk at any time, even if you feel better.

Call 999 even if the person seems better after using the injector. The NHS says anaphylaxis needs to be treated in hospital immediately, where adrenaline, oxygen and fluids may be given, and that people usually stay for around 2 to 12 hours.

The NHS lists the most common allergenic foods as cows’ milk, eggs, peanuts, soybeans, peas and chickpeas, tree nuts (walnuts, almonds, hazelnuts, pecans, cashews, pistachios and Brazil nuts), shellfish (prawns, crab and lobster) and wheat. You can be allergic to any food, including celery, mustard, sesame seeds and lupin flour in some baked goods.

In the UK, food law identifies 14 regulated allergens, which Allergy UK lists as celery, cereals containing gluten, crustaceans, eggs, fish, lupin, milk, molluscs, mustard, peanuts, sesame, soya, sulphur dioxide and sulphites, and tree nuts. By law, information about these must be available for all food sold, including pre-packed and loose foods.

The NHS says you have a slightly higher chance of a food allergy if you or a close family member have other allergies, asthma or eczema. Some people get an itchy mouth and throat after raw fruit, vegetables or nuts, called oral allergy syndrome or pollen food syndrome. The NHS says it is not usually serious and that eating well-cooked fruit and vegetables helps.

Allergy UK divides food allergies into three types according to symptoms and timing. IgE-mediated food allergy is the most common, with symptoms starting a few seconds or minutes after eating. Non-IgE-mediated allergy involves other parts of the immune system and has a delayed onset. Some people have mixed patterns, with immediate symptoms such as hives or swelling and delayed gut or skin symptoms.

The difference matters for testing: blood and skin-prick tests look for IgE, so they are of limited use for delayed reactions, which are usually assessed with a supervised elimination diet and reintroduction.

The NHS advises seeing a GP if you think you or your child may have a food allergy. A GP may refer you to a specialist for tests. The NHS lists a skin-prick test (a drop of liquid containing the food is put on the skin to see if it reacts), blood tests, and a diet that avoids the suspected food to see if symptoms improve, and may ask you to keep a food and symptoms diary.

NICE guideline CG116 covers food allergy in under 19s: assessment and diagnosis, with advice on taking a clinical history, diagnosing IgE and non-IgE food allergy and when to refer to specialist care. NICE says it does not cover reactions due to intolerance. Allergy UK stresses that diagnosing a food allergy matters for preventing severe reactions and avoiding unnecessary dietary restrictions.

The NHS and Allergy UK give the same core advice: know your allergen, check labels, tell people, and carry your medication.

• Check food labels and restaurant menus carefully, and do not eat foods without checking the ingredients.

• Carry 2 adrenaline auto-injectors or nasal sprays at all times if prescribed, and check their expiry dates.

• Tell friends, family, nursery, school, work, restaurant staff and airline cabin staff about your allergy.

• Avoid sharing utensils, plates or cooking surfaces with allergenic foods, to prevent cross-contact.

• Plan ahead for travel and events, taking safe snacks where possible.

• For cafés and take-aways, ask: food businesses must provide allergen information, though how they share it can vary.

On the NHS the route is usually a GP, then a referral to an allergy clinic if a food allergy is suspected. The NHS says a specialist gives you an allergy action plan. NICE CG116 sets out when children and young people should be referred.

Private allergy clinics offer assessment and tests, and some people choose them for quicker appointments. The same principles apply: tests are only meaningful alongside a clinical history, and NHS advice on adrenaline and emergency action is the same whichever route you use. Be cautious about unvalidated tests, particularly home tests that claim to diagnose intolerance.