A strawberry allergy is an IgE-mediated immune response to specific proteins in the fruit. The body mistakenly identifies these proteins as a threat, triggering the release of chemicals that cause allergic symptoms. The question of what else a person might react to is often answered by investigating cross-reactivity, where the immune system confuses similar proteins found in different substances.
The Core Mechanism: Cross-Reactivity and Protein Families
Allergic reactions involve the immune system’s recognition of proteins. In a strawberry allergy, the immune system develops Immunoglobulin E (IgE) antibodies that latch onto specific strawberry proteins. Cross-reactivity occurs when those IgE antibodies encounter a protein in a different substance that is structurally similar to the original strawberry protein, triggering an allergic reaction.
Many plant allergens belong to shared protein families that exist across multiple species. Strawberry allergenic proteins include the Fra a 1 family (Pathogenesis-Related or PR-10 proteins) and the Fra a 3 family (non-specific lipid transfer proteins or ns-LTPs). For example, Fra a 1 proteins are structural homologues of Bet v 1, a major birch pollen allergen. This shared molecular architecture explains why the immune system may react to multiple seemingly unrelated foods.
Foods with Shared Allergenic Proteins
The most direct food-to-food cross-reactivity occurs with other members of the Rosaceae botanical family, which includes strawberries. This family contains many common fruits that share similar allergenic proteins, such as PR-10 and ns-LTPs. A reaction to strawberries may signal a potential for reactions to other fruits within this family.
Stone fruits, also part of the Rosaceae family, are a major group of potential cross-reactors. Their allergenic proteins often share enough similarity with those in strawberries to trigger a reaction. Other close relatives, such as raspberries and blackberries, also belong to Rosaceae and can cause cross-reactive symptoms.
Stone Fruits and Berries
Stone fruits that may cause cross-reactions include:
- Peaches
- Plums
- Cherries
- Apricots
- Almonds
While less common, some nuts and seeds can also share cross-reactive proteins with strawberries. The non-specific lipid transfer proteins (ns-LTPs), specifically Fra a 3, are associated with cross-reactivity to various nuts, including hazelnut, particularly in the Mediterranean region. This type of cross-reactivity is often linked to more systemic allergic reactions.
The Pollen Connection: Oral Allergy Syndrome
A common reason for reactions to strawberries is Oral Allergy Syndrome (OAS), also known as Pollen-Food Allergy Syndrome (PFAS). This IgE-mediated response is rooted in a primary allergy to environmental pollens, not the food itself. The reaction occurs because proteins in raw fruits and vegetables are nearly identical to proteins found in certain pollens, fooling the immune system.
The most frequent link for strawberry allergy is to birch pollen, a common cause of seasonal allergies. Birch pollen contains the allergen Bet v 1, and the strawberry protein Fra a 1 is a structural homologue. This cross-reactivity means a person allergic to birch pollen may experience symptoms when eating raw strawberries. Up to 70% of birch pollen-allergic individuals may develop allergies to various fruits, nuts, or vegetables.
The symptoms of OAS are typically localized and mild, primarily affecting the mouth and throat. Reactions usually involve an itchy or scratchy sensation, or slight swelling of the lips, tongue, or pharynx. Since the allergenic proteins are easily broken down by heat and digestive enzymes, reactions usually occur only when the fruit is eaten raw and rarely progress to a severe systemic reaction.
Common OAS Cross-Reactors
Other common birch pollen-related OAS cross-reactors include:
- Apples
- Carrots
- Celery
- Peaches
Distinguishing True Allergy from Chemical Sensitivity
Not all adverse reactions to strawberries are true IgE-mediated allergies. Some individuals experience symptoms due to a chemical sensitivity or intolerance, which does not involve IgE antibodies.
Strawberries are naturally high in salicylates, a chemical compound also found in aspirin that plants use as a defense mechanism. A sensitivity to salicylates can produce symptoms that mimic a mild allergy, such as hives, rash, digestive issues, or respiratory problems. This reaction is considered a pharmacological response to the chemical, not an immune system malfunction.
A person experiencing salicylate sensitivity reacts to the chemical structure itself, not the protein. If a reaction is due to salicylate sensitivity, the person may also react to other high-salicylate foods, such as certain spices, tomatoes, or apples, even without a cross-reactive protein link.