Botanical Characteristics of Macadamia Nut
- Scientific Names:
- Macadamia integrifolia (Smooth-shelled macadamia)
- Macadamia tetraphylla (Rough-shelled macadamia)
- Family: Proteaceae
- Common Names: Macadamia nut, Queensland nut
- Native Region: Australia (now cultivated in Hawaii, South Africa, and Latin America)
Tree and Fruit Description
- Macadamia trees are evergreen, growing 6–12 meters tall.
- The nut is encased in a hard shell inside a green husk.
- Macadamia nuts are high in monounsaturated fats and commonly used in confections, nut butters, and cooking oils.
Macadamia Nut as a Food Allergen
Unlike other FDA-listed major tree nuts, macadamia nuts have a lower prevalence of allergic reactions. However, documented cases suggest IgE-mediated hypersensitivity in some individuals.
Allergenic Proteins in Macadamia Nuts
| Allergen | Protein family | Molecular weight (kDa) | Clinical relevance |
|---|---|---|---|
| Mac i 1 | Vicilin (7S globulin) | 50 | Storage-protein allergen |
| Mac i 2 | Legumin (11S globulin) | 60 (20 and 40 kDa subunits) | Storage-protein allergen |
Cross-Reactivity
- Its storage proteins are structurally related to those of walnuts, pecans and almonds, but clinical cross-reactivity appears limited; macadamia allergy is often isolated.
- No macadamia lipid transfer protein is officially named, so a link with peach or apple allergy is not established.
- Cross-reactivity with peanut or soy is not established, although reactions in peanut-allergic people have been reported — ask your allergist before eating macadamia.
Detailed epitope (amino-acid) maps previously shown here have been removed because they could not be matched to published studies. Exact epitope positions vary between studies and between patients.
Stability of Macadamia Allergens
| Allergen | Heat stability | Digestive stability | Effect of processing |
|---|---|---|---|
| Mac i 1 | Moderate to high | Moderate | Largely survives roasting |
| Mac i 2 | Moderate to high | Moderate | Largely survives roasting |
- Macadamia storage proteins (Mac i 1, Mac i 2) remain stable, meaning roasted macadamia nuts can still cause reactions.
- Grinding or baking does not make macadamia safe for people who are allergic.
Symptoms of Macadamia Nut Allergy
Reactions range from mild to life-threatening.
Mild Symptoms
- Itchy mouth, tingling lips (with tree nuts this is not pollen-related oral allergy syndrome; it can be the first sign of a severe reaction).
- Hives, skin rash.
- Nausea, vomiting, diarrhea.
Severe Symptoms (Anaphylaxis) Epinephrine (auto-injector or nasal spray) is required for anaphylaxis.
- Swelling of throat (laryngeal edema).
- Difficulty breathing, wheezing.
- Drop in blood pressure (anaphylactic shock).
Diagnosis and Testing
Skin Prick Test (SPT)
- Detects IgE-mediated reactions to macadamia extract.
Serum IgE Testing
- Measures IgE antibodies to macadamia (whole extract).
Oral Food Challenge (OFC)
- Gold standard for confirming allergy.
- Performed under medical supervision.
Anaphylaxis: act fast. After an exposure, any breathing symptom (wheeze, repeated cough, throat tightness, hoarse voice), fainting or dizziness, or symptoms in two or more body systems (for example hives plus vomiting) is anaphylaxis — even without hives.
- Give epinephrine right away (auto-injector or nasal spray). Do not wait to see if symptoms get better.
- Call 911, even if symptoms improve.
- Lie flat with legs raised (sit up if breathing is hard). Give a second dose after 5–15 minutes if there is no improvement.
Antihistamines and steroids do not treat anaphylaxis and must never delay epinephrine. Carry two doses and follow the written emergency action plan from your allergist.
Management and Prevention
Avoidance Strategies
- Read labels → Macadamia nuts are in chocolates, baked goods, nut butters.
- Cross-contamination risks → Often processed with walnuts, almonds.
Emergency Treatment
- Epinephrine (auto-injector or nasal spray).
- Antihistamines may ease mild skin symptoms such as itching or hives, but they do not treat anaphylaxis and must never delay epinephrine.
- Corticosteroids are sometimes given by doctors after a reaction, but they do not treat anaphylaxis and have not been shown to prevent a second-wave (biphasic) reaction.
Immunotherapy
- Oral Immunotherapy (OIT) is being studied for macadamia allergy desensitization.
Comparison with Other Tree Nuts
| Nut | Key allergens (WHO/IUIS) | Strongest clinical cross-reactivity | Stability | Anaphylaxis risk |
|---|---|---|---|---|
| Almond | Pru du 6 (legumin), Pru du 3 (LTP); Pru du 1 (PR-10) | Among the least cross-reactive tree nuts | Storage proteins and LTP stable; PR-10 labile | High |
| Brazil nut | Ber e 1 (2S albumin), Ber e 2 (legumin) | Often an isolated allergy | Stable | High |
| Cashew | Ana o 3 (2S albumin), Ana o 1 (vicilin), Ana o 2 (legumin) | Pistachio — very high | Stable | High |
| Hazelnut | Cor a 9 (legumin), Cor a 14 (2S albumin); Cor a 1 (PR-10) | Birch pollen (Cor a 1, usually mild) | Cor a 9/14 stable; Cor a 1 labile | High with Cor a 9 or Cor a 14 sensitization |
| Macadamia | Mac i 1 (vicilin), Mac i 2 (legumin) | Often an isolated allergy | Stable | High |
| Pecan | Car i 1 (2S albumin), Car i 2 (vicilin), Car i 4 (legumin) | Walnut — very high | Stable | High |
| Pine nut | Pin p 1 (2S albumin) | Often an isolated allergy | Stable | High — many reported reactions are anaphylaxis |
| Pistachio | Pis v 1 (2S albumin), Pis v 2 and Pis v 5 (legumin), Pis v 3 (vicilin) | Cashew — very high | Stable | High |
| Walnut | Jug r 1 (2S albumin), Jug r 2 (vicilin), Jug r 4 (legumin); Jug r 3 (LTP) | Pecan — very high | Stable | High |
- Macadamia allergy is less common than walnut or pecan allergy but can still cause severe reactions, including anaphylaxis.
- Macadamia allergy is often isolated; cross-reactivity with other nuts appears limited.
Conclusion
- Macadamia nuts contain allergens (Mac i 1, Mac i 2) that can trigger IgE-mediated reactions.
- Clinical cross-reactivity with other tree nuts appears limited, and no link with Rosaceae fruits is established.
- Roasting does not eliminate allergenicity.
- Severe reactions require epinephrine preparedness.