Adult-onset allergy occurs when symptoms suddenly appear after years of living without them. This phenomenon is surprisingly common, affecting a significant portion of the adult population. In the United States, nearly half of adults with a food allergy report that at least one allergy began later in life. Understanding why the body begins to react to previously harmless substances requires looking at shifts within the immune system and changes in external exposures.
The Mechanism of Adult Allergy Development
The sudden onset of an allergy results from sensitization, the body’s misidentification of a harmless substance as a threat, centered on Immunoglobulin E (IgE). IgE is an antibody produced by specialized B cells in response to an allergen. The first exposure causes the immune system to create specific IgE antibodies that travel through the bloodstream and attach to mast cells, which are concentrated in tissues like the skin, lungs, and gastrointestinal tract. The mast cells are now sensitized. When exposed again, the allergen binds to the IgE on the mast cell surface, causing the cell to rapidly release inflammatory chemicals, such as histamine, which causes the immediate symptoms of an allergic reaction, like sneezing, itching, or swelling.
External Factors That Trigger New Sensitivities
The tipping point for this immune shift is often a change in a person’s environment or internal balance, leading to sensitization. Moving to a new geographic location, for instance, exposes the immune system to entirely different local flora and fauna, such as new types of pollen or mold spores. A person may suddenly develop seasonal allergies because their immune system is encountering novel proteins for the first time.
Environmental pollution is also linked to allergic diseases, as air particles can damage the protective epithelial barriers of the airways and skin. This damage allows allergens to penetrate more easily and initiate the sensitization process.
Changes in lifestyle and internal regulation also play a role in initiating new allergies. Chronic stress affects the immune system by altering hormone levels, such as cortisol, which can deplete the body’s ability to moderate the inflammatory response. Furthermore, fluctuations in reproductive hormones, such as those occurring during pregnancy or menopause, can alter immune function and trigger new sensitivities.
Specific Types of Allergies That Appear in Adulthood
Specific allergic conditions frequently emerge for the first time in adults.
Oral Allergy Syndrome (OAS)
Oral Allergy Syndrome (OAS), also known as pollen-food syndrome, is a common example that develops in people who already have seasonal allergies. This condition is a result of cross-reactivity, where IgE antibodies created to fight tree or weed pollen mistakenly recognize similar proteins in certain raw fruits, vegetables, or nuts. Symptoms are typically limited to itching or tingling in the mouth and throat after eating the offending food.
Adult-Onset Food Allergies
Adult-onset food allergies can develop suddenly to foods eaten safely for years, with shellfish, tree nuts, and peanuts being among the most common triggers. Unlike OAS, which is usually mild, these new food allergies carry the risk of a severe, systemic reaction.
Other Late-Onset Allergies
Another type of late-onset allergy involves drug reactions, which may occur after repeated exposure to a medication like an antibiotic or pain reliever. Contact dermatitis, a delayed-type hypersensitivity reaction, can also appear in adulthood, often triggered by new occupational exposures or products containing substances like nickel or certain chemicals.