Allergies occur when the immune system mistakenly identifies a harmless substance, such as pollen or a food protein, as a threat. This misidentification triggers a cascade of reactions intended to fight off an invader. The body’s sensitivity can shift at any point in life, meaning new allergies can indeed develop in adulthood.
Confirming Adult-Onset Allergies
The development of allergies later in life is a medically recognized phenomenon known as adult-onset allergy. While many people associate allergic disease only with childhood, a significant portion of the adult population experiences the first appearance of allergic symptoms long after their youth. Studies have shown that nearly half of adults diagnosed with a food allergy developed at least one of those sensitivities during their adult years.
It is important to distinguish between a truly new allergy and the re-emergence of a dormant one. A new allergy involves the immune system becoming sensitized to a substance it previously tolerated. In contrast, some childhood allergies, such as those to milk or egg, may fade only to have the underlying sensitivity return years later due to new environmental or internal factors.
Triggers for Developing New Sensitivities
The immune system’s shift to an allergic state in adulthood results from a combination of biological and environmental pressures. One factor is the cumulative exposure to a specific substance over time, which can eventually push the immune system past its tolerance threshold. Moving to a new geographic location, for example, can introduce the body to unfamiliar types of pollen, initiating a sensitization process that leads to seasonal allergies.
Major hormonal changes can also modulate immune function, particularly in women, making them more susceptible to developing new sensitivities. Events such as pregnancy, perimenopause, or menopause involve significant fluctuations in sex hormones like estrogen and progesterone. Estrogen, in particular, can enhance immune activity and increase the body’s production of histamine, the chemical responsible for many allergic symptoms.
Viral infections can sometimes act as an unexpected trigger by temporarily or permanently altering immune pathways. Severe infections, including certain strains of the flu or viruses like Epstein-Barr and COVID-19, can irritate the immune system’s “allergy branch.” This irritation can cause the immune system to become hyper-reactive, leading to new allergic responses to previously safe environmental or food triggers.
Changes in microbial exposure are another theoretical cause, often discussed under the “Hygiene Hypothesis.” This concept suggests that reduced exposure to a diverse range of microbes early in life prevents the immune system from maturing fully. This lack of microbial training can lead to an imbalance in T-helper cells, making the immune system more likely to initiate an allergic response to harmless substances later in life.
Common Late-Life Allergic Reactions
Adult-onset allergies often manifest with specific triggers that differ from the typical allergies seen in children. Among the most common late-life sensitivities are new food allergies, with shellfish, tree nuts, and finned fish being frequent culprits. Unlike some childhood food allergies that are outgrown, those that develop in adulthood tend to persist and can sometimes be severe.
Another common presentation is Oral Allergy Syndrome, also known as pollen-food syndrome. This reaction involves the mouth or throat itching after eating raw fruits, vegetables, or nuts because the proteins in the food are structurally similar to the proteins found in certain pollens. Adults often develop sensitivities to medications they previously tolerated, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or certain antibiotics.
Late-onset seasonal allergies, or allergic rhinitis, are also a frequent complaint, manifesting as hay fever symptoms like congestion and sneezing that suddenly appear in one’s 30s or 40s. Additionally, repeated, high-level exposure in the workplace can lead to occupational allergies, such as a sensitivity to latex or flour dust, which develop due to chronic contact with the allergen.
Testing and Treatment Approaches
If new allergic symptoms appear, consulting a specialist is the first step toward accurate diagnosis and management. Allergists typically use skin prick tests, which involve placing a small amount of allergen extract just beneath the skin’s surface, to identify immediate sensitivities. Blood tests are also frequently used to measure the level of immunoglobulin E (IgE) antibodies specific to suspected allergens.
For food allergies, a supervised oral food challenge, conducted in a medical setting, may be necessary to confirm the diagnosis. Once an allergy is confirmed, the primary management strategy is strict avoidance of the trigger. Symptoms for mild reactions can often be managed with over-the-counter or prescription antihistamines.
For more persistent environmental allergies, immunotherapy, administered as allergy shots or under-the-tongue drops, can be used to desensitize the immune system over time. Individuals diagnosed with severe allergies that carry a risk of anaphylaxis must be prescribed and trained to use an epinephrine auto-injector.