Nut allergy in adults: symptoms, diagnosis and what to do in anaphylaxis

Epidemiological data on adults are scarcer than for children, but allow several conclusions. A large survey from the USA covered more than 40 thousand adults and showed that food allergy is widespread in adulthood too, and that a substantial proportion of cases begin only after reaching adulthood.

For Poland European data are useful. The EuroPrevall project covered adults in several cities, including Łódź, and showed large geographical differences: the frequency of 'probable' food allergy ranged from 0.3% in Athens to 5.6% in Zurich, and was 2.8% in Łódź. In Łódź, Utrecht and Zurich the commonest foods provoking symptoms were hazelnut, peach and apple, and oral symptoms were reported by 81.6% of people with allergy. It is worth noting that in these populations a very large share of 'hazelnut allergy' is cross-allergy with pollen, not a primary allergy to the nut.

American and European data cannot be compared directly and do not settle how often nut allergy begins in adults in Poland. We stress that the 48% figure concerns food allergies overall, not nuts alone. What is known is that reviews devoted to tree nuts describe these allergies as usually severe, beginning in childhood and often persisting throughout life.

Adults with very different histories come to the allergist's office. The first group are people with an allergy to peanuts or tree nuts that began in childhood and did not resolve. Such allergies more often involve several nuts and require constant caution and an emergency plan. The second group are adults in whom the allergy appeared only in adult life: after years without symptoms a reaction to a nut suddenly appears, often in the context of other allergies, including pollen allergy.

A review devoted to food-triggered anaphylaxis in adults notes that food allergy in adults, both persisting from childhood and new-onset, is increasingly prevalent, and that foods matter as triggers of anaphylaxis in people of all ages. Peanuts are among those mentioned, and so are additional factors (cofactors), which are becoming ever more relevant, especially with sensitisation to LTP and wheat. The authors stress that anaphylaxis in adults should not be dismissed as 'idiopathic' before unusual triggers and cofactors have been considered.

The practical conclusion for the reader: a new reaction after nuts in adult life deserves full allergological work-up, not the assumption that 'it is only pollen'. What decides between mild oral allergy syndrome and the more dangerous primary allergy is the sensitisation profile, established with component tests (discussed below).

Peanuts (groundnuts) are botanically the seeds of a legume, not tree nuts, but in clinical practice and on labels they are often mentioned together. Tree nuts include hazelnuts, walnuts, cashews, almonds, pistachios, pecans, macadamias and Brazil nuts, among others. Sensitisation to one kind does not automatically mean sensitisation to all, but certain pairs of nuts cross-react exceptionally often.

Anaphylaxis is an acute, systemic allergic reaction that can be life-threatening. It usually begins within minutes to two hours of exposure to the allergen and may involve the skin (urticaria, flushing, swelling), the respiratory system (shortness of breath, wheezing, throat swelling), the circulation (dizziness, fall in blood pressure, fainting) and the gastrointestinal tract (vomiting, cramping abdominal pain). Not all symptoms need occur, and urticaria may be absent, especially in a severe course.

The points above are general and do not replace the individual advice of a doctor or the instructions for a specific device, which differ between manufacturers. The EAACI guidelines recommend that people at risk of anaphylaxis undergo structured training. If you have a nut allergy and no management plan, this is a topic to discuss with an allergist first.

Diagnosis begins with the history: which nut, in what form, after how long, what symptoms, whether there was exercise, alcohol or an infection, whether there is pollen allergy. IgE sensitisation is then assessed: skin prick tests and the concentration of specific IgE. Positive results alone indicate sensitisation, not clinical allergy, and may be positive in people who eat nuts without symptoms.

The EAACI guidelines on diagnosing IgE-mediated food allergy indicate that measuring IgE specific to allergen components, such as Ara h 2 (peanut), Cor a 14 (hazelnut) or Ana o 3 (cashew), can help confirm the diagnosis, especially in pollen-sensitised people. The oral food challenge is the reference standard and should be performed in equivocal cases, in a centre prepared to treat severe reactions, never on your own at home.

Several conclusions follow for adults with nut allergy. Avoidance remains the basis, but only of the nuts that actually provoke reactions: the review by Jeong and Lee recommends a pragmatic approach that allows tolerated nuts to be included in the diet. This is important, because excluding 'all nuts' is needlessly restrictive if diagnostics have shown sensitisation to only some of them. Oral immunotherapy is in the EAACI guidelines recommended for children and adolescents with peanut allergy, not for adults, whereas for adults omalizumab is suggested for consideration in selected cases, which is a decision for an allergy centre.

What we do not know: data for Poland are limited and we rely on European and American studies, which need not reflect the Polish population. There are no reliable data on the frequency of newly diagnosed nut allergy in adulthood in our country. The guidelines cited above rest partly on low-quality evidence, especially as regards emergency treatment. We do not describe the availability of drugs or reimbursement rules, because we do not rely on sources confirming that information. The article does not replace an individual plan from an allergist.

Nut allergy in adults needs two things at once: reliable diagnostics, which distinguish a dangerous primary allergy from a mild cross-allergy with pollen, and readiness for a sudden reaction. The first reduces needless dietary restrictions, the second protects against the worst scenario. There is no need to choose between them.