The human immune system is a dynamic network that continually adapts to its environment. While many people develop allergies early in life, the immune system can shift its focus and begin reacting to previously harmless substances in adulthood. This phenomenon is known as adult-onset allergy, where the body mistakenly identifies a benign protein as a threat, triggering an allergic reaction. The development of a new allergy later in life demonstrates that the immune response is not fixed, but can be reprogrammed by various internal and external factors over time.
Common Categories of Adult-Onset Allergies
New food allergies are among the most frequently reported types to emerge in adulthood. Shellfish, including shrimp, crab, and lobster, is a common culprit that suddenly causes reactions in people who have consumed them for years without issue. Tree nuts and peanuts also trigger new, sometimes severe, immune responses in adults.
Another category is Oral Allergy Syndrome, also known as Pollen-Food Allergy Syndrome (PFAS). This typically develops in those who already have a sensitivity to pollen. The reaction occurs because the immune system recognizes similar protein structures in raw fruits, vegetables, and some nuts, causing symptoms like itching or tingling in the mouth and throat after consumption.
Environmental or inhalant allergies are the most common overall type of new sensitivity that develops in adults. These can manifest as perennial allergies to indoor triggers like dust mites, pet dander, or mold, causing year-round symptoms such as chronic nasal congestion and sneezing. New seasonal allergies, or hay fever, can also start unexpectedly, with the immune system reacting to tree, grass, or weed pollen.
The third major type is allergic contact dermatitis, a skin reaction that occurs when the body develops a hypersensitivity to a substance that touches the skin. Common triggers include metals like nickel, often found in jewelry, or chemicals in cosmetics, personal care products, and latex. This immune response causes an itchy, red rash, which may take several days to appear after contact with the allergen.
Mechanisms Driving New Allergic Sensitivities
The shift in the immune system that allows for new allergies to form is influenced by multiple interacting factors. Changes in environmental exposure play a significant role, as moving to a new geographic region introduces the immune system to different local pollens, molds, and other allergens it has never encountered before. New exposures in the workplace or introducing a pet into the home can also push the immune system past a threshold of tolerance.
Internal biological changes, particularly hormonal fluctuations, can also influence the body’s allergic state. Significant life events, such as pregnancy or menopause, involve substantial hormonal shifts that can alter immune system regulation in women, sometimes leading to the onset of new sensitivities. The cumulative effect of aging, known as immunosenescence, involves a gradual change in how the immune system functions, which may increase its susceptibility to new allergic sensitization.
The concept of losing immune tolerance is another theory explaining adult-onset allergies. This may be linked to changes in the gut microbiome, which is a collection of microorganisms that helps regulate immune responses throughout the body. An imbalance in this microbial environment can potentially affect the immune system’s ability to tolerate certain food or environmental proteins. Furthermore, a severe viral or bacterial infection can sometimes act as a trigger, altering the immune system’s response to previously tolerated substances.
Identifying and Addressing Late-Life Allergies
A person should see a specialist if they experience sudden or severe symptoms after exposure to a known or suspected trigger. A medical evaluation is important if symptoms suggest a systemic reaction, such as difficulty breathing, swelling of the tongue or throat, or a rapid drop in blood pressure. These signs could indicate anaphylaxis, which requires immediate emergency medical attention.
Identifying the specific allergen begins with diagnostic tools, most commonly a skin prick test or a specific Immunoglobulin E (IgE) blood test. A skin prick test involves placing a small amount of allergen extract on the skin and monitoring for a localized reaction. The IgE blood test measures the amount of allergy-specific antibodies in the bloodstream. For suspected food triggers, a doctor may also recommend a temporary elimination diet to confirm the link between a food and the symptoms.
Initial management strategies center on avoiding the identified trigger to prevent future reactions. For environmental allergies, over-the-counter antihistamines and nasal steroid sprays are common steps to alleviate symptoms like sneezing and congestion. If the allergy has the potential to cause a severe reaction, such as a new food or insect venom allergy, the physician will prescribe an epinephrine auto-injector for emergency use.