An allergy is a misdirected response by the body’s immune system, which mistakenly identifies a typically harmless substance—such as pollen or a food protein—as a threat. This overreaction leads to the production of Immunoglobulin E (IgE) antibodies, which trigger the release of chemicals like histamine that cause allergic symptoms. The immune system’s allergic status is not fixed from birth; rather, it is a dynamic state that shifts throughout a person’s lifetime. Therefore, it is possible to both acquire new sensitivities and lose old ones as the body ages and its environment changes.
The Reality of Adult-Onset Allergies
New sensitivities can unexpectedly develop in adulthood, a phenomenon often termed adult-onset allergy, which can occur even to substances consumed for years without issue. This development happens through a process called sensitization, where the immune system, after sufficient exposure, begins to produce IgE antibodies against a previously tolerated protein. For nearly half of food-allergic adults, at least one of their allergies began later in life.
One of the most common adult-onset allergies is seasonal allergic rhinitis, or hay fever, which can begin in a person’s twenties or thirties. This often results from new or prolonged exposure to environmental allergens like pollen, mold spores, or dust mites. Food allergies also frequently emerge in adulthood, with shellfish and tree nuts being among the most common culprits in these later-life cases.
An adult-onset food allergy, such as a sudden reaction to shrimp or walnuts, is generally less likely to disappear than a childhood food allergy. Furthermore, allergies to medications, such as antibiotics or pain relievers, and sensitivities to substances like latex can also arise for the first time in an adult.
Developing Tolerance to Childhood Allergens
While new allergies can develop, the reverse process, known as developing tolerance or outgrowing an allergy, is common, particularly in pediatric cases. Tolerance occurs when the immune system stops recognizing an allergen as a threat, effectively ending the allergic response. The likelihood of this happening is highly dependent on the type of allergen involved.
Allergies to milk, egg, soy, and wheat are the most frequently outgrown childhood food allergies. For instance, a significant majority, approximately 60% to 80% of children, will outgrow their milk or egg allergies, often by the time they reach their teenage years. This regression is thought to relate to the maturation of the immune system and the body’s ability to process these protein structures over time.
In contrast, allergies to peanuts, tree nuts, fish, and shellfish are much more likely to persist throughout life. Only about 20% to 25% of children with a peanut allergy will outgrow it, and even fewer—around 4% to 5%—will lose their sensitivity to fish or shellfish. The proteins in these latter allergens tend to be more stable and potent, making the IgE-mediated response more permanent.
Environmental and Biological Factors Driving Allergy Changes
The dynamic nature of allergies is a consequence of both environmental pressures and biological shifts within the body. Changes in geographic location can introduce the immune system to entirely new flora and fauna, such as different tree or grass pollens, leading to sensitization and the onset of seasonal allergies. Similarly, increased exposure to high concentrations of indoor allergens, such as adopting a new pet, can trigger a new allergic response.
Internal biological changes also play a significant role in modulating the immune response. Hormonal fluctuations, notably those occurring during puberty or pregnancy, have been implicated in either the onset or the temporary remission of allergic symptoms. Furthermore, the composition of the gut microbiome, the trillions of microorganisms residing in the digestive tract, is known to influence the immune system’s overall balance and sensitivity.
This concept is partly captured by the “Hygiene Hypothesis,” which suggests that reduced exposure to microbes and infections early in life may prevent the immune system from developing a balanced response. Shifts in diet, increased exposure to air pollution, and modern Westernized lifestyles can contribute to changes in the microbiome. These changes may promote immune dysregulation that predisposes an individual to new allergies.