A peanut allergy is an overreaction by the immune system to specific proteins found in peanuts, primarily storage proteins like Ara h 1, 2, and 3. When an allergic person consumes peanuts, their body mistakenly identifies these proteins as a threat, triggering the production of immunoglobulin E (IgE) antibodies. This IgE-mediated response releases inflammatory chemicals, such as histamine, which cause the characteristic allergic symptoms. While this condition is traditionally associated with onset during infancy or early childhood, developing this hypersensitivity later in life is possible. Research is increasing into whether an adult can suddenly become allergic to a food they have safely eaten for years.
Adult-Onset Peanut Allergy Is Possible
Yes, an adult can develop a new allergy to peanuts later in life. Recent epidemiological data demonstrates that a notable number of adult-onset cases occur, challenging the view that this allergy is exclusively pediatric. One large-scale survey found that approximately 17% of US adults with a peanut allergy reported the onset of their condition after turning 18 years old. This suggests that over 800,000 adults in the US may have developed their peanut allergy during adulthood. Although adult-onset food allergies are often associated with shellfish and fin fish, peanuts are also among the most frequently reported allergens in new adult cases.
Understanding the Triggers for Adult Onset
The mechanisms causing a previously tolerant adult to become allergic are not fully understood, but several factors play a role. The immune system is constantly evolving, and a loss of oral tolerance—the body’s normal non-response to food proteins—can occur at any age. This loss may be prompted by environmental or biological shifts that cause the immune system to become sensitized to peanut protein.
Cross-Reactivity
One significant pathway involves cross-reactivity, specifically with tree pollens, known as Pollen-Food Allergy Syndrome. Individuals allergic to birch pollen, for example, may develop symptoms upon eating certain fruits or vegetables containing proteins structurally similar to the pollen allergens. This sensitization to related proteins, such as Ara h 8, can sometimes precede a more severe, IgE-mediated reaction to the primary peanut storage proteins.
Environmental and Biological Shifts
Environmental factors and changes in the body’s internal state may also contribute. Some patients report the onset of their allergy coinciding with a viral infection, significant antibiotic use, or hormonal changes. Increased exposure to peanuts in new forms, or a period of reduced exposure followed by reintroduction, may also tip the balance toward sensitization. The specific peanut proteins that trigger a reaction, such as Ara h 9 in some adult patients, can differ from the typical triggers in childhood-onset cases.
Recognizing Symptoms and Diagnosis in Adults
The symptoms of a new-onset peanut allergy in adults are consistent with any IgE-mediated food allergy, ranging from mild to potentially life-threatening. Common signs include skin reactions like hives, swelling of the lips, face, or throat, and itching or tingling in the mouth. Gastrointestinal issues such as nausea, vomiting, or stomach cramps can also occur. Severe reactions, including difficulty breathing, wheezing, a rapid pulse, or a sudden drop in blood pressure, indicate anaphylaxis and require immediate emergency intervention.
Diagnosis can be challenging because adults may dismiss initial symptoms as stress, food intolerance, or a passing illness. A clinician will begin by taking a detailed medical history, focusing on the type and amount of food ingested, the onset and duration of symptoms, and the presence of other allergic conditions.
To confirm the diagnosis, specific tests are utilized, including skin prick tests (SPT) and IgE blood tests. A positive skin prick test or a high level of peanut-specific IgE antibodies suggests sensitization, but these tests alone do not definitively prove a clinical allergy. The most reliable method for confirmation is a supervised oral food challenge (OFC). During an OFC, the patient consumes gradually increasing amounts of peanut protein under strict medical observation to see if a reaction occurs. This procedure helps differentiate a true IgE-mediated allergy from a non-allergic food sensitivity.
Managing a New Adult Peanut Allergy
Once a peanut allergy is confirmed, management centers on rigorous avoidance and preparedness for accidental exposure. The primary strategy involves total avoidance of peanuts and all peanut-containing products, requiring careful attention to food labels and questioning at restaurants. Adults must learn to identify hidden sources of peanut protein and be wary of cross-contamination.
Carrying an epinephrine auto-injector is a necessary safety measure, as allergic reactions are unpredictable and can escalate to anaphylaxis. Patients must be educated on how to recognize the signs of a severe reaction and how to correctly administer the epinephrine into the outer thigh. Adults with new-onset allergies are often less likely to have a prescription for an auto-injector than those with childhood-onset allergies.
Consultation with a board-certified allergist is important for ongoing care, risk assessment, and exploring treatment options. While avoidance is standard, some adults may be candidates for oral immunotherapy (OIT), which involves consuming gradually increasing doses of peanut protein under medical supervision to build tolerance. Seeking support or counseling for the mental health aspects of this chronic condition is also an important part of the overall management plan.