An allergen is a substance that triggers an immune reaction in some individuals, despite being harmless to most people. These substances are common in our environment, yet for certain individuals, they can cause a range of symptoms from mild discomfort to severe, life-threatening responses. Understanding how these everyday substances can become problematic is the first step toward managing their impact on one’s health.
What are Allergens?
When a sensitive person encounters an allergen, their immune system responds by producing specific antibodies, primarily immunoglobulin E (IgE). This immune response leads to an allergic reaction.
The body’s reaction can manifest in various ways, depending on where the allergen enters the body. For instance, inhaling pollen might cause respiratory symptoms, while consuming certain foods could lead to digestive issues. These reactions result from the immune system’s attempt to neutralize a substance it perceives as a threat.
Common Categories of Allergens
Allergens can be broadly categorized by their source and how they enter the body.
Airborne Allergens
These are inhaled into the respiratory system. Examples include pollen from trees, grasses, and weeds, which cause seasonal allergies like hay fever. Dust mites, microscopic creatures found in household dust, as well as pet dander (tiny flakes of skin, saliva, or urine from animals) and mold spores, are frequent airborne triggers that can cause year-round symptoms.
Food Allergens
These substances provoke an allergic reaction upon ingestion. The “Big Nine” food allergens, responsible for most food allergies in the United States, include:
- Milk
- Eggs
- Peanuts
- Tree nuts (such as almonds, walnuts, and cashews)
- Fish
- Shellfish (like shrimp, crab, and lobster)
- Wheat
- Soy
- Sesame
Reactions to these can range from mild digestive upset to severe systemic responses.
Other Allergens
Insect stings, particularly from bees, wasps, hornets, yellow jackets, and fire ants, can cause allergic reactions due to venom. Certain medications, such as penicillin and other antibiotics, are also known allergens. Contact allergens, like nickel in jewelry or latex, can cause skin reactions when they come into direct contact with the skin.
How Allergens Trigger Reactions
When an allergen first enters the body, a process called sensitization occurs. During this initial exposure, the immune system produces immunoglobulin E (IgE) antibodies. These IgE antibodies then attach to specialized immune cells called mast cells, which are abundant in tissues lining the body’s surfaces, such as the skin, airways, and digestive tract, and basophils in the bloodstream.
Upon subsequent exposure to the same allergen, the allergen binds to the IgE antibodies on mast cells and basophils. This binding signals these cells to release various chemicals, including histamine. Histamine is a chemical mediator that causes many allergy symptoms, such as increased blood flow, inflammation, itching, and mucus production. Other chemicals like prostaglandins and leukotrienes are also released, further contributing to the allergic response.
Identifying and Managing Allergies
Identifying specific allergens often begins with a review of a person’s symptoms and their relation to exposure. Diagnostic methods include skin prick tests, where a small amount of suspected allergen extract is applied to the skin, typically on the forearm or back, and the skin is gently pricked. A positive reaction, indicated by a raised, red, itchy bump within 15 to 20 minutes, suggests an allergy. Blood tests, specifically IgE blood tests, measure the presence of IgE antibodies in the bloodstream specific to certain allergens. These tests are useful when skin tests are not feasible, for instance, if a person is taking allergy medications or has certain skin conditions.
Managing allergies involves several strategies, with avoidance of known allergens being the primary and most effective measure. Individuals with food allergies must strictly avoid consuming the problematic food. Over-the-counter medications relieve symptoms; antihistamines like cetirizine or loratadine block the effects of histamine, reducing itching, sneezing, and runny nose. Nasal corticosteroids such as fluticasone address nasal congestion and inflammation.
For severe reactions, especially a life-threatening response called anaphylaxis, immediate medical attention is required, and an epinephrine auto-injector is administered. Immunotherapy, also known as allergy shots, involves exposing the body to gradually increasing doses of an allergen to build tolerance. This long-term treatment can significantly reduce or eliminate allergy symptoms and may prevent the progression of allergic diseases like asthma.