Food allergies, while often associated with childhood, can emerge at any point in life, a phenomenon known as adult-onset food allergy. This article explores the characteristics of adult-onset food allergies and the underlying biological and environmental reasons for their emergence.
Understanding Adult-Onset Food Allergies
Adult-onset food allergies involve an IgE-mediated immune system response that appears for the first time in adulthood. These reactions occur when the immune system mistakenly identifies a harmless food protein as a threat, producing specific IgE antibodies against it. Upon subsequent exposure, these antibodies trigger the release of chemicals like histamine, leading to allergic symptoms.
While food allergies are more prevalent in children (affecting an estimated 8%), they also affect a significant portion of the adult population, with estimates around 5% to 10.8% in the United States. A 2019 study indicated that almost half of U.S. adults with food allergies developed at least one new allergy after age 18. Adult-onset food allergies can be as severe as those experienced in childhood, sometimes leading to life-threatening reactions like anaphylaxis.
Key Factors Behind Development
The development of food allergies in adulthood is a complex process influenced by changes in the immune system, environmental exposures, lifestyle factors, and genetic predispositions. Immune system changes can play a role, particularly disruptions to the gut microbiome. A healthy gut typically has a diverse range of bacteria, and reduced bacterial diversity has been linked to increased susceptibility to allergies. Antibiotic use, which can disrupt healthy gut bacteria, and modern sanitation practices, reducing exposure to various microbes, might contribute to this decreased diversity, leading the immune system to react to substances that should be harmless.
Environmental and lifestyle shifts can also trigger adult-onset allergies. New dietary exposures, such as consuming foods not regularly eaten before, might lead to sensitization. Factors like stress and certain medications (e.g., antibiotics, antacids) can alter gut pH and microbiome composition, potentially influencing immune tolerance. Exposure to environmental allergens or pollutants (e.g., traffic pollution, passive smoking) may also increase the risk of sensitization to food allergens.
Genetic predisposition also contributes, though it does not always manifest in childhood. While genetics can make an individual more susceptible to allergies, environmental triggers often play a role in their development later in life. Studies on twins suggest a genetic component, with a higher incidence of shared food allergies in identical twins. The interplay between genes and environmental exposures is complex and continuously being researched.
Cross-reactivity is another mechanism where an existing allergy can lead to new food allergies. This commonly occurs in Oral Allergy Syndrome (OAS), also known as Pollen-Food Allergy Syndrome (PFAS). In OAS, proteins in certain raw fruits, vegetables, or nuts are structurally similar to proteins found in pollen, causing the immune system to react to the food. For instance, individuals allergic to birch tree pollen might react to apples or cherries due to similar protein structures. Symptoms are often limited to the mouth and throat, but can occasionally be more severe.
Common Adult-Onset Allergens
Several foods are frequently associated with allergies that first appear in adulthood. Shellfish (including crustaceans like shrimp, lobster, and crab, along with mollusks) are among the most common adult-onset allergens. Finned fish also commonly trigger new allergies. Tree nuts and peanuts are frequent culprits, similar to their prevalence in childhood. While some childhood allergies (e.g., milk, egg, soy, wheat) can be outgrown, allergies to fish and shellfish often develop in adulthood or persist. Fruits and vegetables, especially those involved in Oral Allergy Syndrome, are also common adult-onset allergens, often due to cross-reactivity with pollen.
Allergy vs. Intolerance
Distinguishing between a food allergy and a food intolerance is important, as they involve different bodily mechanisms. A food allergy is an immune-mediated response where the immune system identifies specific food proteins as harmful. This response typically involves IgE antibodies, leading to the release of chemicals like histamine, which can cause symptoms ranging from mild skin reactions to life-threatening anaphylaxis. Even a small amount of the allergenic food can trigger a severe reaction.
In contrast, a food intolerance does not involve the immune system. It typically arises from the body’s inability to properly digest or metabolize a food component, often due to enzyme deficiencies. Lactose intolerance, caused by a lack of the lactase enzyme needed to break down lactose, is a common example. Symptoms of intolerance are generally less severe than allergies, often localized to the digestive system, and may include bloating, gas, or diarrhea. Symptoms also tend to appear more gradually and are often dose-dependent, meaning small amounts might be tolerated.