A stone fruit allergy is an adverse immune system reaction to specific proteins found in certain fruits. A true food allergy involves the immune system mistakenly identifying a food component as a threat, triggering a protective response. This condition can range from minor mouth irritation to potentially life-threatening systemic reactions like anaphylaxis. The cause lies in the unique structure and stability of the proteins within the fruit itself.
The Stone Fruit Family and Reaction Types
Stone fruits belong to the Prunus genus within the Rosaceae family of plants. They are characterized by having a hard pit, or “stone,” in the center that encloses a single seed. Common examples include peaches, plums, nectarines, cherries, and apricots. Almonds are also part of this family, and individuals allergic to stone fruits may react to them.
Reactions generally fall into two categories based on the stability of the allergenic protein. The most common is a localized reaction, often restricted to the mouth and throat, which is typically mild. The second, less common but more concerning, is a systemic reaction affecting multiple organ systems.
The Role of Lipid Transfer Proteins
The primary cause of severe, systemic stone fruit allergies is the presence of Lipid Transfer Proteins (LTPs), such as Pru p 3 in peaches. These highly stable molecules serve a defense function in the plant. Their compact structure makes them resistant to both heat and the acidic environment of the stomach.
Because LTPs survive cooking and the digestive process, they travel intact through the gastrointestinal tract and enter the bloodstream, leading to a systemic allergic reaction. Sufferers must avoid the fruit in all forms, including raw, cooked, dried, or processed products like jams and juices. This allergy is frequently observed in adults and is the most common cause of food allergy in Southern Europe.
LTP allergy is associated with a higher risk of anaphylaxis and can involve co-factors. Co-factors, such as exercise, alcohol, or NSAIDs, can trigger or worsen a reaction. These factors lower the reaction threshold, meaning a smaller amount of protein is needed to cause a severe response. This severe reaction is not dependent on a pre-existing pollen allergy.
Link to Pollen Allergies and Cross-Reactivity
A more common mechanism for stone fruit allergy involves cross-reactivity with environmental allergens, known as Oral Allergy Syndrome (OAS). This reaction occurs in people sensitized to certain tree pollens, particularly birch pollen. The immune system mistakenly recognizes the fruit proteins as the pollen proteins it is already allergic to.
The proteins responsible for OAS are primarily PR-10 proteins, which are structurally similar to the major birch pollen allergen, Bet v 1. Unlike stable LTPs, PR-10 proteins are heat-labile, meaning they are easily broken down by cooking or stomach acid. This instability is why OAS symptoms are typically confined to the mouth and throat and rarely progress to a systemic reaction.
Symptoms of OAS include tingling or itching in the mouth, lips, and throat immediately after eating the raw fruit. Because the protein is destroyed by heat, individuals with OAS can often safely consume cooked forms of stone fruit, such as in pies or canned products. This heat-sensitivity distinguishes the milder OAS from the more serious LTP-driven allergy.
Recognizing and Responding to Reactions
Mild reactions, characteristic of OAS, include immediate itching or tingling in the mouth, a scratchy throat, or slight swelling of the lips and tongue. These symptoms usually resolve quickly once the fruit is swallowed or removed.
In contrast, a systemic reaction caused by stable LTPs can progress to severe, life-threatening symptoms known as anaphylaxis. Signs of anaphylaxis include difficulty breathing, wheezing, a rapid and weak pulse, dizziness, or a sudden drop in blood pressure. Hives, vomiting, or stomach pain may also occur.
Immediate action is mandatory if a severe reaction is suspected. If a person has been prescribed an epinephrine auto-injector, it must be used immediately by injecting the medication into the outer thigh. Emergency medical services must be called right away, even after using epinephrine, as the individual needs medical observation.
Diagnosis and Long-Term Avoidance Strategies
Formal diagnosis begins with a detailed medical history, focusing on the timing and nature of symptoms after eating the fruit. Allergy testing confirms the presence of specific IgE antibodies in the blood. The main diagnostic tools are the skin prick test and a blood test measuring IgE antibody levels.
A more advanced technique called Component-Resolved Diagnostics (CRD) can differentiate between allergenic proteins, such as stable LTPs (Pru p 3) and heat-labile PR-10 proteins (Pru p 1). This testing helps an allergist determine if the allergy is a mild OAS or a potentially severe, LTP-driven sensitivity. This distinction is necessary for creating an effective management plan.
Long-term management centers on strict avoidance of the trigger fruit, including carefully reading food labels. Individuals with severe LTP allergy must avoid the fruit in all forms. Those with milder OAS may tolerate cooked or peeled stone fruits, but all individuals at risk of systemic reaction must carry a prescribed epinephrine auto-injector.