Allergies are often misunderstood as conditions exclusively developed in childhood. In fact, allergies can begin at any point in life, a phenomenon often referred to as adult-onset allergy. An allergy is an overreaction by the body’s immune system to a substance that is otherwise harmless, such as pollen or a specific food protein. The immune system mistakenly identifies this substance, known as an allergen, as a threat and generates Immunoglobulin E (IgE) antibodies. IgE then triggers the release of chemicals like histamine, which cause the physical symptoms of an allergic reaction.
Understanding Immune System Shifts
The immune system changes throughout an individual’s life, and these age-related alterations influence the development of new allergies. One mechanism involves immune senescence, which describes the gradual changes and dysfunction in the immune system that occur with aging. This process can disrupt the balance of immune regulation, potentially leading to a hyper-responsive state where the body overreacts to previously tolerated substances.
This heightened sensitivity can also be explained by the concept of a cumulative exposure threshold. Even if an individual has been exposed to an allergen for years without issue, the body may eventually reach a point where the total exposure crosses a sensitization threshold, causing the immune system to recognize the substance as a threat. Major life events can also temporarily or permanently alter immune function. Hormonal fluctuations, severe illness, or periods of intense stress can all impact the body’s immune regulation, potentially triggering an allergic response.
Environmental changes also play a large part in the sudden appearance of adult allergies. Moving to a new geographic region exposes the body to a different profile of local flora, fauna, and molds, which may contain novel allergens. Increased exposure to airborne pollutants and environmental shifts due to climate change, like warmer and longer seasons, can also increase the concentration of common allergens like mold spores and pollen. These factors can push a sensitized individual past their symptom threshold.
Common Types of Adult-Onset Allergies
While any substance can become an allergen, certain types of allergies frequently begin in adulthood. Adult-onset food allergies are notable, with almost half of affected adults reporting that at least one developed later in life. The most common food triggers include shellfish (such as shrimp and crab), peanuts, tree nuts, and finned fish.
A common type of reaction seen in adults is Oral Allergy Syndrome (OAS), also known as Pollen-Food Allergy Syndrome (PFAS). This condition involves an allergic reaction to certain raw fruits or vegetables because their proteins are structurally similar to the proteins found in certain pollens, such as birch or ragweed. Symptoms are typically confined to the mouth and throat, causing immediate itching and tingling, though severe reactions are possible.
Seasonal allergies, or allergic rhinitis, are also a frequent adult-onset condition. An individual may suddenly begin experiencing hay fever symptoms after moving to an area with different tree, grass, or weed pollens, or simply due to years of cumulative exposure to local allergens. Beyond environmental and food triggers, new sensitivities to medications or chemicals can also arise. Reactions to drugs, even those previously tolerated, are possible, with common examples including antibiotics like penicillin or non-steroidal anti-inflammatory drugs.
Symptoms and When to Seek Diagnosis
Recognizing the symptoms of a true IgE-mediated allergic reaction is important for timely diagnosis and management. Typical allergic symptoms have a rapid onset, appearing within minutes to a few hours of exposure, and can affect multiple organ systems. Skin reactions are common, manifesting as raised, itchy hives (urticaria), facial swelling (angioedema), or generalized redness and itching.
Respiratory symptoms can include nasal congestion, a runny nose, sneezing, or a scratchy throat, but more concerning signs involve the lower airway, such as wheezing, coughing, or difficulty breathing. The most severe reaction is anaphylaxis, a life-threatening, systemic event that can include a sudden drop in blood pressure, dizziness, persistent vomiting, or constriction of the airways. It is important to distinguish these immune-driven reactions from a food intolerance, such as lactose intolerance, which typically involves only digestive symptoms like cramping or nausea and does not involve the IgE antibody.
Any experience of a rapid, multi-system reaction warrants a consultation with an allergist. Self-diagnosis or simply avoiding the suspected trigger is insufficient, as professional testing is needed to accurately identify the specific allergen and determine the risk of a severe reaction. Diagnostic tools usually include a skin prick test, where small amounts of allergens are introduced to the skin surface, or a blood test to measure allergen-specific IgE antibodies. Identifying the trigger allows for an effective management plan, which may involve avoidance strategies, prescription medication, or carrying an emergency adrenaline auto-injector.