Developing an allergy later in life is possible. An allergy represents an overreaction by the body’s immune system to a substance, known as an allergen, that is typically harmless to most people. This phenomenon of developing new sensitivities in adulthood is common, affecting various body systems. Genetic predisposition and changes in environmental exposure are thought to play a significant role in causing the immune system to suddenly perceive a previously tolerated substance as a threat.
The Immune Mechanism Behind Developing New Allergies
Developing an allergy involves a two-step immunological process known as sensitization. The first step occurs upon initial exposure when the immune system mistakenly identifies an allergen as a foreign invader. Specialized immune cells produce allergen-specific antibodies called Immunoglobulin E (IgE). These IgE antibodies circulate and attach themselves to mast cells, which reside in tissues like the skin, lungs, and gastrointestinal tract.
This initial exposure “primes” the mast cells for a future encounter. The second step triggers the allergic reaction upon re-exposure to the substance. The allergen binds to the IgE antibodies anchored to the mast cell surface. This cross-linking signals the mast cell to rapidly degranulate, releasing powerful inflammatory chemicals, most notably histamine.
Histamine is responsible for the familiar symptoms of an allergic reaction, such as itching, swelling, and hives. Sensitization can increase with repeated exposure, potentially leading to more severe reactions over time. This mechanism explains why tolerance can last decades before the immune system undergoes sensitization and reacts aggressively years later.
Common Categories of Adult-Onset Allergies
Food is one of the most common categories of newly developed allergies in adults. Shellfish, including shrimp and crab, and tree nuts are frequently cited culprits for adult-onset food allergies. A 2019 study suggested that approximately half of adults with a food allergy reported that at least one of their allergies developed after childhood.
Oral Allergy Syndrome (OAS), also called Pollen Food Allergy Syndrome, often appears later in life. This condition occurs in people who are already allergic to certain pollens, such as birch or ragweed. Their immune system recognizes similar protein structures in specific raw fruits, vegetables, or nuts. When these foods are eaten, the reaction is usually confined to the mouth, causing symptoms like an itchy throat or tingling sensation.
Allergies to medications can manifest suddenly, even after a person has tolerated the drug for years. Common examples include antibiotics, such as penicillin and sulfa-based medications. Environmental and occupational exposures also frequently trigger adult-onset sensitivities. Moving to a new geographic area can introduce unfamiliar pollens from local flora, leading to seasonal allergies for the first time.
New-onset pet allergies are also possible, often developing after years of cumulative exposure to animal dander in a household. The actual allergens are proteins found in the pet’s saliva, urine, and skin flakes, which cause symptoms like a runny nose or watery eyes.
When to Seek Professional Diagnosis and Care
If new symptoms appear involving itching, hives, swelling, or difficulty breathing, seek professional medical guidance immediately. Persistent symptoms, such as chronic nasal congestion, coughing, or gastrointestinal distress that interfere with daily activities, also warrant evaluation. A healthcare professional can determine if the symptoms are caused by a true IgE-mediated allergy or by another condition, such as a food intolerance.
Distinguishing between an allergy and an intolerance is important. An allergy involves the immune system and can be life-threatening, while an intolerance involves the digestive system and is typically less severe. The diagnostic process begins with a detailed medical history and may include specific tests to identify the trigger.
The most common diagnostic tool is the skin prick test, where a small amount of allergen extract is placed on lightly scratched skin. The development of a raised, red bump (a wheal) indicates sensitivity to that substance. Alternatively, a specific IgE blood test can measure the level of allergen-specific IgE antibodies in the blood. Identifying the exact allergen is the first step toward creating a management plan involving avoidance strategies, medication, or immunotherapy.