Allergies

Abstract

During an allergic reaction, the immune system reacts to normally harmless foreign substances such as pollen, medications, food, or animal dander. Although allergic reactions can principally take place in all organs, the primary target organs are the skin, respiratory system, gastrointestinal tract, and eyes. Depending on the organs involved, symptoms of allergic reactions include nasal congestion, eczema, pruritus, cough, chest tightness, wheezing, dyspnea, and vomiting. In case of anaphylaxis, a potentially fatal severe allergic reaction, cardiovascular changes resulting in hypotension and tachycardia can additionally occur. Allergic diseases are characterized by immune responses predominantly driven by T-helper-2 (T_h2) cells, which activate many immune cells to produce and release different inflammatory mediators during an allergic reaction (see chapter “Overview” under the part “Immune system”). Apart from allergen avoidance, the treatment principles are neutralization of these mediators particularly in the short term and restoration of immune balance between T_h2 cells and other lymphocyte subsets like T-helper-1 (T_h1) or regulatory T (T_reg) cells in the long term. The risk factors include family history of allergy/genetic factors and environmental factors such as exposures to allergens and microbes. However, a number of studies show conflicting data for the latter, suggesting that the interaction of certain allergens and infectious agents with the immune system is complicated. Nonetheless, a dramatic increase in allergic diseases in industrialized countries over the last several decades implicates environmental factors as a major contributor. Allergic diseases affect up to 30 % of the population in these countries, resulting in high economical burden of the diseases.

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