The confusion between peanuts and hazelnuts is common because both are grouped together for culinary purposes and often appear in similar food products. However, a hazelnut is not a peanut; they belong to completely different plant families. Understanding this distinction is significant, especially for consumers managing food allergies, where mistaking one for the other can have severe health consequences. Their differing biological origins and protein structures necessitate a clear understanding of their botanical classification and how regulatory bodies address their presence in food.
Botanical Identity: Hazelnut vs. Peanut
Peanuts and hazelnuts stem from distinct botanical groups, making them fundamentally different organisms. Peanuts (Arachis hypogaea) are classified as legumes, belonging to the Fabaceae family, which also includes beans, peas, and lentils. Peanuts develop underground in a pod, a characteristic known as geocarpy.
Hazelnuts, in contrast, are true tree nuts, growing on trees from the Corylus genus, such as Corylus avellana. A true nut is a hard-shelled fruit that does not split open to release its seed at maturity, a criterion the hazelnut meets. Peanuts are an annual herbaceous plant, while hazelnuts grow on woody perennial trees, highlighting a major difference in their life cycles.
Both are commonly called “nuts” due to culinary tradition rather than scientific classification. They share similar flavor profiles and applications in cooking, leading to their commercial grouping. However, the scientific distance between the Fabaceae family (peanuts) and the Betulaceae family (hazelnuts) is vast.
Allergy Implications and Cross-Reactivity
The botanical difference translates directly into differences in the specific proteins that trigger allergic reactions. Both allergies are IgE-mediated, meaning the immune system overreacts to specific proteins, but the structure of these allergenic proteins varies between legumes and tree nuts. Peanut allergy is linked to storage proteins like Ara h 1, Ara h 2, and Ara h 3, while hazelnut allergy involves proteins such as Cor a 9, Cor a 11, and Cor a 14.
Individuals can be allergic to both peanuts and hazelnuts, a situation known as co-sensitization. Studies indicate that 20 to 40 percent of individuals with a peanut allergy also have a clinical allergy to at least one tree nut, with hazelnut being a common co-allergen. This co-occurrence is complex and is not always due to simple cross-reactivity between the major storage proteins.
Some hazelnut allergens, like Cor a 1, show structural similarity to the major birch pollen allergen, Bet v 1. This similarity can lead to pollen-food allergy syndrome, often presenting as oral symptoms.
Due to the high rate of co-sensitization, medical guidance frequently recommends caution or avoidance of all nuts until specific testing is performed. The type of protein involved is important, as some hazelnut proteins are heat-sensitive, meaning roasted hazelnuts might be tolerated, while others remain stable and pose a severe risk.
Food Labeling and Safety Regulations
Regulatory frameworks in the United States recognize the distinction between peanuts and tree nuts for consumer safety. The Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) mandates clear labeling for the most common food allergens, often called the “Major 9.” Significantly, peanuts are listed as a separate category from the group of tree nuts, which includes hazelnut, almond, and walnut.
FALCPA requires that the food source of any major allergen must be listed on the product label in one of two ways. Manufacturers must list the allergen either in parentheses following the ingredient name or in a clear “Contains” statement immediately after the ingredient list. When hazelnut is used, the label must specify the common name, such as “hazelnut” or “filbert,” rather than just listing “tree nuts.”
Consumers should also look for advisory statements, such as “may contain” or “processed in a facility with,” which address the risk of unintentional contamination, or cross-contact. While not mandatory under FALCPA, many manufacturers use these voluntary warnings. Peanuts and tree nuts are often processed on shared equipment, presenting a contamination risk for both groups.