New allergies can develop unexpectedly during adulthood, a phenomenon known as adult-onset allergy. This sudden appearance is surprising because the immune system begins reacting to substances previously tolerated for many years. This article explores the biological process that allows these changes and the factors that can trigger this shift in your body’s response.
How the Immune System Develops New Sensitivities
The immune system’s response to an allergen occurs in two distinct phases, explaining why the reaction seems to happen “all of a sudden.” The first phase is sensitization, where the immune system encounters a harmless allergen but mistakenly identifies it as a threat. During this initial exposure, the body shows no outward symptoms.
Specialized immune cells stimulate the production of Immunoglobulin E (IgE) antibodies. These IgE antibodies are tailored to recognize that particular allergen and attach themselves to the surface of mast cells, which are immune cells located in tissues throughout the body. This process effectively arms the mast cells, preparing them for a future invasion.
The second phase is the reaction phase, occurring upon subsequent exposure to the same allergen. When the allergen enters the body again, it binds to the IgE antibodies coating the armed mast cells. This causes the mast cells to rupture and release chemical mediators, most notably histamine, which is responsible for familiar allergy symptoms like sneezing, itching, and swelling.
The “sudden” allergic reaction is the immune system’s second, highly visible response to an allergen it was quietly sensitized to sometime prior. This sensitization period can last for months or even years without the person being aware of the change.
Environmental and Hormonal Factors That Drive Sudden Onset
Many external and internal changes can push a mature immune system past its tolerance threshold, initiating the sensitization process. A common external factor is a major environmental shift, such as relocating to a new geographic area with different types of pollen, mold spores, or dust mites. Increased exposure to airborne pollutants and changes in climate patterns that lengthen the pollen season can also contribute to a heightened immune response.
Internal changes can also lower the immune system’s barrier to sensitization. Significant hormonal fluctuations, particularly in women, are a known trigger, with allergy onset sometimes coinciding with periods like pregnancy or menopause. These hormonal shifts can temporarily recalibrate the immune system’s overall function.
A significant viral infection can temporarily alter the immune system’s regulatory balance, sometimes leading to new sensitivities after the illness passes. Prolonged stress or changes in the gut microbiome due to diet or medication use are additional factors. Often, a combination of these factors—such as a new environment coinciding with high stress or illness—tips the scale toward an allergic reaction.
The Most Common Allergens That Appear Later in Life
While an adult can develop an allergy to any substance, certain allergens are frequently implicated in adult-onset cases. Among food allergies, shellfish, such as shrimp and lobster, and tree nuts are common triggers for new reactions in adults. Studies suggest that approximately half of adults with a food allergy developed at least one of them later in life.
Environmental allergies, often called hay fever, can also begin in adulthood. Common culprits include:
- Pollen from trees and grasses
- Pet dander
- Mold spores
A specific food-related reaction that frequently appears in adulthood is Oral Allergy Syndrome (OAS), also known as Pollen Food Allergy Syndrome (PFAS). This occurs when a person with an existing pollen allergy reacts to raw fruits, vegetables, or nuts because their proteins are similar to the proteins in the pollen.
OAS symptoms are typically confined to the mouth and throat, causing immediate itching or tingling. Medications, including antibiotics and pain relievers, and substances like latex, especially with increased occupational exposure, are other common categories where new sensitivities can emerge in adulthood.
When to Seek Professional Diagnosis and Management
If you experience new or worsening symptoms such as persistent sneezing, chronic nasal congestion, hives, or tingling in the mouth after eating, consult a healthcare provider or an allergist. A proper diagnosis confirms if the reaction is a true allergy, involving the IgE mechanism, or a non-allergic intolerance, which uses a different biological pathway.
Allergy testing, typically involving skin prick tests or specific IgE blood tests, can accurately identify the substance causing the reaction. Skin prick tests introduce a tiny amount of the allergen under the skin, while blood tests measure IgE antibodies in the bloodstream.
Management begins with precise identification of the trigger and allergen avoidance. Treatment may involve over-the-counter or prescription antihistamines for mild symptoms. For those at risk of a severe reaction, an epinephrine auto-injector prescription is necessary. In cases of persistent environmental allergies, an allergist may recommend immunotherapy, which desensitizes the immune system over a period of years.