What Causes Allergies?
Frederick R. Jelovsek MD, MS When your nose is runny and eyes are itchy you probably are just interested in relief; not in why this reaction is happening. Sometimes though, it is helpful to know the detail of how a medical condition is produced especially when it is one that is chronic and going to afflict you the rest of your life. Allergy is one such condition. People with allergies have genes that make them more likely to develop a bodily reaction to various substances they are exposed to.
People with allergies have an inherited (genetic) predisposition for developing hypersensitivity to inhaled and ingested substances (allergens) that are harmless to other people. A healthy immune system is balanced between the activity of 2 types of white blood cells, called Th1 and Th2. • Genetic or environmental factors can cause a Th2 dominated response to develop which can lead to allergies. • The use of immunizations and antibiotic therapies and increased pollution leads to Th2 dominance. • Once an imbalance in T cells develops, it tends to be continued by production of chemicals (cytokines) that keep the imbalance in place.
You have an allergy when your body overreacts to things that don’t cause problems for most people. These things are called allergens. Your body’s overreaction to the allergens is what causes symptoms (see the box below for a list of symptoms). For example, sometimes the term “hay fever” is used to describe your body’s allergic reaction to seasonal allergens in the air, such as grass or pollen. Your doctor may want to do an allergy skin test to help determine exactly what is causing your allergy. An allergy skin test puts tiny amounts of allergens onto your skin to see which ones you react to. Once you know which allergens you are allergic to, you and your doctor can decide the best treatment. Your doctor may also decide to do a blood test, such as the radioallergosorbent test (called RAST).
