Tree nut allergy: symptoms, testing, labelling and managing reactions

A food allergy occurs when the immune system wrongly identifies a food as a threat and releases chemicals such as histamine. The NHS lists tree nuts, such as walnuts, almonds, hazelnuts, pecans, cashews, pistachios and Brazil nuts, among the most common allergenic foods, alongside cows' milk, eggs, peanuts, shellfish and wheat.

Anaphylaxis UK explains that tree nuts come from different plant families to peanuts, so many people react to peanuts but not tree nuts, and vice versa. Within the tree nuts, many people are allergic to only one type, though it is quite common for people allergic to cashew nuts also to be allergic to pistachios, and for walnut allergy to go with pecans.

A different pattern can occur in people with hay fever. Anaphylaxis UK describes a secondary nut allergy known as pollen food syndrome, caused by cross-reactivity between pollen and nut proteins, most commonly involving hazelnuts, almonds and peanuts. Reactions are very rarely serious and often involve itching or swelling in the mouth. The NHS makes the same point about an itchy mouth and throat after eating raw fruit, vegetables or nuts.

Anaphylaxis UK says symptoms of peanut and tree nut allergy usually come on quickly, within minutes of eating. Mild to moderate symptoms include a red raised itchy rash (hives), swelling of the face, lips or eyes, tingling or itching in the mouth, mild throat tightness, stomach pain, vomiting or diarrhoea.

The more serious reaction is anaphylaxis. Healthcare professionals consider a reaction to be anaphylaxis when it involves difficulty breathing or affects the heart rhythm or blood pressure. Anaphylaxis UK groups the signs as airway, breathing and circulation problems, summarised below. The NHS adds that symptoms can sometimes appear days later rather than straight after eating, which is another reason to keep a diary of foods and symptoms.

Anaphylaxis UK gives three clues that someone may be at higher risk of a more serious reaction: having already had a serious reaction with any of the ABC symptoms, having asthma, especially if it is not well controlled, and reacting to a tiny amount of nut. Poorly controlled asthma can make an allergic reaction worse, so taking prescribed asthma medicines and reviewing control with a GP or allergy specialist is part of managing the allergy.

The NHS also notes a slightly higher chance of food allergy if you or a close relative have other allergies, asthma or eczema.

If you think you or your child may be allergic to tree nuts, see your GP. Anaphylaxis UK advises that the GP can refer you to a specialist allergy clinic and that it is important to get a referral even if the symptoms were mild. The consultant will discuss your history and may suggest skin prick tests, blood tests and food challenge tests. If you have reacted to one nut, tests are likely to include a range of nuts to establish which are safe.

The NHS describes the skin-prick test as a drop of liquid containing the food placed on the skin to see if it reacts, blood tests, and a supervised diet in which the food is avoided to see whether symptoms improve. It advises keeping a food and symptoms diary. Be wary of unvalidated tests marketed directly to the public, and ask whether any test you are offered is accepted by NHS allergy clinics.

Once diagnosed you will need to avoid the nuts you are allergic to. Anaphylaxis UK explains that peanuts and tree nuts are among the top 14 major allergens in the UK, which means they must be highlighted on ingredient labels, for example in bold. It advises reading the ingredient list every time you buy a product because recipes change. Restaurants, cafes and takeaways are required by law to provide information on major allergens, and you should ask staff directly about nuts and cross-contamination and explain that small amounts can cause a reaction.

Foods that often contain nuts include satay and pesto sauces, marzipan, praline, salads and dressings, cakes, biscuits and pastries, muesli and granola, cereal bars, chocolates, ice cream and some vegetarian, vegan and gluten-free products. Tree nut oils should be avoided too, and in cosmetics tree nuts are labelled using Latin names.

The same factsheet suggests eating nuts you are not allergic to, since this may help avoid developing allergy to them, but only after testing and specialist advice, and being careful about cross-contamination in packets of mixed nuts.

• Check the label every time, even for familiar products.

• Tell friends, family, school and workplace about the allergy.

• Ask in restaurants about the specific dish, not just the menu.

• Keep a copy of your allergy action plan where carers and teachers can see it.

The NHS says to call 999 if lips, mouth, throat or tongue suddenly swell, if breathing is very fast or hard, if the throat feels tight or swallowing is difficult, if skin, tongue or lips turn blue, grey or pale, or if someone becomes very confused, drowsy or dizzy, or faints. Do not drive yourself to A&E. If you have an adrenaline auto-injector such as an EpiPen, or the nasal spray EURneffy, use it immediately, then call 999 even if you feel better.

Anaphylaxis UK adds that you must carry two in-date forms of prescribed adrenaline at all times, because a second dose may be needed if symptoms do not improve after five minutes or get worse. Antihistamines may be prescribed for mild reactions, but they are not a treatment for anaphylaxis. Your specialist should give you an allergy action plan that explains what to do.

NHS care starts with the GP, then a specialist allergy clinic for testing, an action plan and prescriptions for adrenaline devices. Dietitians with allergy experience may advise on safe eating and on whether other nuts can be reintroduced. Anaphylaxis UK points to the British Society for Allergy and Clinical Immunology to find clinics.

Private consultant allergists can offer quicker appointments and testing. If you consider this route, check the specialist's training, ask which tests will be used and why, ask who will prescribe adrenaline and review your action plan, and ask for a written summary to share with your GP and your child's school or nursery.