A hazelnut allergy is an adverse immune response to the proteins found in hazelnuts, a type of tree nut. The immune system mistakenly identifies these proteins as harmful, triggering the release of chemicals that cause allergic symptoms. Reactions can range from mild discomfort to a life-threatening event, similar to other tree nut allergies.
Prevalence Among Tree Nut Allergies
Hazelnuts (filberts) are a significant cause of food allergy globally, though their ranking varies by region. In Europe, hazelnut is often reported as the most common tree nut allergy, sometimes reaching a self-reported prevalence of 4.0%, particularly when accounting for cross-reactivity with pollen.
However, in the United States, the most common tree nut allergies are typically cashew and walnut, with hazelnut following alongside almond. The prevalence of a clinically confirmed hazelnut allergy in the US pediatric population is estimated to be around 0.2% to 0.5%.
The overall prevalence of IgE-mediated tree nut allergy confirmed by oral food challenge is less than 2% of the population. While the number of people allergic to peanuts is consistently higher than any single tree nut, 20% to 30% of those with a peanut allergy are also allergic to at least one tree nut, including hazelnut.
The higher frequency of hazelnut allergy in Europe is partially attributed to the widespread presence of birch pollen, which creates a unique sensitization pattern.
Unique Reaction Patterns and Oral Allergy Syndrome
Hazelnut allergy presents with two distinct reaction patterns. The first involves primary sensitization to stable storage proteins, such as Cor a 9 and Cor a 14. These proteins are resistant to heat and digestion, making them likely to survive in the gut and trigger severe, systemic reactions. Symptoms of this primary allergy include hives, swelling of the face or throat, vomiting, difficulty breathing, and potential anaphylaxis.
The second, and often more common, pattern is Pollen Food Allergy Syndrome (PFAS), previously known as Oral Allergy Syndrome (OAS). This reaction is caused by cross-reactivity between the heat-sensitive hazelnut protein Cor a 1 and the major birch pollen allergen, Bet v 1. Because the immune system recognizes the structural similarity, a person allergic to birch pollen may also react to raw hazelnut. This pattern is particularly common in areas with high birch tree populations.
Symptoms of OAS are typically localized and milder, affecting the mouth and throat. People may experience an itching or tingling sensation in the mouth, throat, or lips almost immediately after eating raw hazelnuts. Since the Cor a 1 protein is broken down by heat and stomach acid, individuals with OAS can often safely eat roasted or baked hazelnuts. This is generally not true for those with the more severe, primary allergy.
Confirming the Diagnosis
Confirming a hazelnut allergy requires diagnosis to differentiate between reaction types and establish the risk of a severe event. A healthcare provider begins with a detailed clinical history of reactions following hazelnut consumption. This is followed by diagnostic testing, which commonly involves skin prick tests (SPTs) and specific IgE blood tests.
The skin prick test involves placing a small amount of hazelnut extract on the skin and lightly pricking the area to see if a raised bump (wheal) develops. Specific IgE blood tests measure the amount of allergy-specific antibodies in the bloodstream. Both tests indicate sensitization, meaning the immune system has produced IgE antibodies against the nut’s proteins, but they do not definitively prove a clinical allergy.
To confirm a true clinical allergy, an oral food challenge (OFC) is often performed. This procedure involves consuming gradually increasing amounts of hazelnut under strict medical supervision in a controlled setting. The OFC provides the most accurate assessment of whether a person will react to hazelnut and the potential severity, guiding the long-term management plan.
Living with Hazelnut Allergy
The primary management strategy for a diagnosed hazelnut allergy is strict avoidance. This requires careful attention to food labels, especially since hazelnuts are sometimes listed as “filberts.” In the United States, the FASTER Act mandates that all packaged foods regulated by the FDA must clearly declare all major food allergens, including the “tree nuts” category, on the label.
Hazelnuts are found in many processed foods, making label reading essential. Common sources include:
- Nut spreads
- Chocolates, cookies, and baked goods
- Certain coffee flavorings
Cross-contamination is a serious risk, especially in facilities that process multiple types of nuts, shared kitchen environments, or ice cream parlors. Individuals must be vigilant about questioning ingredients in restaurants and when consuming foods without a clear label.
For those at risk of a systemic reaction, an emergency action plan developed with a physician is necessary. This plan details the steps to take in case of accidental exposure, including the immediate use of an epinephrine auto-injector (EpiPen). Epinephrine is the medication for treating anaphylaxis, and prompt administration is life-saving, followed by seeking immediate medical attention.