It is possible to develop new allergies later in life, a phenomenon often referred to as adult-onset allergy. Allergies are an overreaction of the immune system to a substance that is typically harmless, such as pollen or peanuts. This immune response involves the production of specialized antibodies called Immunoglobulin E (IgE), which mistakenly flag the substance as a threat. These sensitivities can emerge suddenly, affecting people who have lived for decades without any allergic symptoms.
Why the Immune System Changes Later in Life
The biological mechanisms that govern the immune system do not remain static throughout life. Aging contributes to a process known as immune senescence, which describes the gradual decline and remodeling of immune function. This senescence leads to a loss of the body’s ability to distinguish between harmless and dangerous foreign substances.
As the body ages, there is an imbalance in the population of immune cells, specifically a decrease in new, naive lymphocytes and an accumulation of older memory cells. This shift can promote a skewing of the adaptive immune response toward a Type 2 helper T-cell (Th2) profile, which drives IgE sensitization and allergic reactions. This process of “breaking tolerance” occurs when the immune system loses its ability to recognize a previously tolerated substance as safe.
Hormonal fluctuations, particularly in women, also influence immune regulation. During perimenopause and menopause, changes in estrogen and progesterone levels can intensify allergic responses. Estrogen can stimulate mast cells, the cells that store and release histamine, increasing the body’s overall allergic sensitivity. The decrease of progesterone, which has natural anti-inflammatory properties, removes a calming influence on the immune system, leading to heightened reactivity.
Common Allergies That Start in Adulthood
Food allergies are notably frequent in adult-onset cases, with nearly half of adults reporting a food allergy having developed at least one later in life. The most common culprits include shellfish, such as shrimp and crab, followed by tree nuts, peanuts, and fin fish.
A common form of adult-onset food sensitivity is Oral Allergy Syndrome, also known as Pollen Food Syndrome. This condition is a cross-reactivity where the immune system, already sensitized to pollen, reacts to similar proteins found in raw fruits or vegetables. For example, a person allergic to birch pollen may experience an itchy mouth or throat after eating an apple or carrot.
Adults can also develop allergies in response to workplace exposures, categorized as occupational allergies. These account for a portion of all adult-onset asthma cases, ranging from 9 to 25 percent. Exposures can involve high molecular weight agents, like animal dander in laboratory settings, or low molecular weight chemicals, such as toluene diisocyanate used in polyurethane manufacturing or cleaning agents.
Environmental and Lifestyle Factors in Onset
A common trigger for new allergic responses is a change in geographical location, which exposes the body to new types of local flora and pollen. Moving may introduce the immune system to allergens it has never encountered, such as mountain cedar pollen in the Southwest or specific molds.
Pollution from urban environments is another recognized trigger that can increase allergic sensitization. Exposure to air pollutants like fine particulate matter (PM2.5) and nitrogen dioxide (NO2) can increase inflammation in the airways, making the respiratory system more vulnerable to allergens. These pollutants act as irritants that lower the threshold for an allergic reaction.
Lifestyle choices also play a role through their impact on the gut microbiome, which houses a large portion of the body’s immune cells. A diet high in processed foods or the use of certain medications, such as antibiotics, can disrupt the balance of gut bacteria. This disruption may impair the gut’s barrier function, contributing to the development of new food sensitivities. Chronic stress and obesity are also recognized as factors that can alter immune regulation.
Diagnosis and Initial Management
If new or persistent symptoms like sneezing, hives, or digestive issues appear, it is important to seek a professional diagnosis from an allergist. An allergist will begin with a detailed medical history and may recommend specific testing. Common diagnostic methods include skin prick tests, where small amounts of allergens are introduced to the skin to observe a reaction.
Alternatively, a specific IgE blood test, which measures the amount of allergy-causing antibodies in the blood, may be performed. Modern specific IgE tests are used to quantify the body’s immune response to individual allergens. Identifying the trigger is the first step toward effective management.
Initial steps for the newly diagnosed adult include rigorously avoiding the identified allergen. For milder symptoms, over-the-counter antihistamines and nasal corticosteroid sprays can provide relief. For any patient diagnosed with a new food or drug allergy, particularly one that involves breathing difficulty or swelling, carrying an epinephrine auto-injector is necessary to treat a severe, life-threatening reaction known as anaphylaxis.