A food allergy occurs when the immune system mistakenly identifies a harmless food protein as a threat, triggering an allergic response. Reactions to tree nuts and peanuts are among the most common and potentially severe. While these conditions are often associated with childhood, the immune system can become sensitized to new allergens at any point in life. Developing a severe nut allergy as an adult, even after years of safely consuming nuts, is a documented possibility.
The Reality of Adult-Onset Nut Allergies
Contrary to the common belief that food allergies are exclusively a childhood concern, a significant portion of food allergies are first diagnosed in adulthood. Research suggests that almost half of all adults with a food allergy developed at least one of them later in life. Tree nuts are a frequent trigger, indicated in one study as the second most common allergen after shellfish in newly diagnosed adult patients.
The prevalence of adult tree nut allergy has seen a notable increase, rising from an estimated 0.5% to 1.8% in a recent period. It is important to distinguish between peanuts, which are legumes, and tree nuts, such as walnuts, almonds, and cashews. Both peanut and tree nut allergies can manifest for the first time in adults, requiring awareness regardless of past dietary history.
Understanding the Triggers and Risk Factors
The immune system is constantly evolving, explaining how a person can become allergic to a food they have eaten without issue for decades. One proposed mechanism involves changes in the gut microbiome, known as dysbiosis, where the balance of intestinal bacteria shifts. This alteration can disrupt the gut barrier function, leading the immune system to misidentify previously tolerated food proteins as foreign invaders.
Major systemic changes, such as a severe viral infection or another illness, may also alter the programming of the immune system. Hormonal shifts, like those occurring during pregnancy or menopause, are another factor that can affect immune reactivity. These events can create an environment where the body becomes hypersensitive, leading to the production of Immunoglobulin E (IgE) antibodies against a specific food protein.
A separate, common pathway for adult-onset nut reactions is Oral Allergy Syndrome (OAS), also called pollen-food allergy syndrome. This condition occurs when the immune system, already sensitized to environmental pollens like birch, mistakenly identifies similar proteins found in some nuts, fruits, or vegetables. This cross-reactivity is a frequent cause of new allergic symptoms in adults, often presenting as a milder reaction confined to the mouth and throat. People with existing allergic conditions, such as asthma or eczema, may have an increased risk of developing new allergies later in life.
Recognizing Signs and Symptoms
Allergic reactions to nuts in adults can vary widely in severity, often beginning suddenly after exposure. Mild symptoms may include itching or tingling in the mouth, throat, or ears, a runny nose, or mild hives on the skin. Mild gastrointestinal distress, such as stomach discomfort, nausea, or vomiting, may also occur.
More widespread symptoms can involve swelling of the lips, eyes, or face, along with generalized hives or a rash. These reactions can progress rapidly to severe, life-threatening symptoms known as anaphylaxis. Anaphylaxis is characterized by difficulty breathing due to airway constriction, wheezing, and a feeling of throat tightness or a hoarse voice.
The most severe reactions include a sudden, dangerous drop in blood pressure, leading to dizziness, lightheadedness, or loss of consciousness. Any new or sudden symptoms following the consumption of nuts must be treated as a medical emergency. Even if a previous reaction was mild, subsequent exposures can trigger a far more serious response.
Diagnosis and Management Strategies
If a nut allergy is suspected, the first step is consulting an allergist, who will take a detailed medical history regarding the timing and nature of the symptoms. The diagnostic process involves specific tests to determine if the immune system has produced IgE antibodies against nut proteins.
Diagnosis Methods
A skin prick test involves placing a small amount of the allergen on the skin and pricking the surface to check for a localized raised bump, which indicates sensitization. A blood test measures the level of IgE antibodies in the bloodstream, providing further evidence of an allergy. In some cases, an allergist may recommend a supervised oral food challenge, where small, increasing amounts of the suspected nut are consumed in a controlled medical setting.
Management
The cornerstone of managing a diagnosed nut allergy is strict avoidance of the trigger food. This requires diligent label reading, as peanuts and tree nuts are common ingredients in many packaged foods and can be hidden in unexpected items. Individuals with a confirmed nut allergy must carry an epinephrine auto-injector, which delivers a dose of adrenaline to counteract severe allergic reactions. Knowing how to use this device immediately at the first sign of anaphylaxis is necessary, as it can be life-saving.