What causes allergic reactions?
Whether it's runny, itchy or stuffed, your nose knows what's bothering it. But do you know what's wrong with your nasal passages? Understanding allergies isn't difficult, but it is the first step toward building a healthy alliance with your nose, eyes, lungs, and sinuses.
Allergies are the result of the immune system's mistaken response to a harmless substance. Normally, the immune system stands guard and defends your body against intruders that can be dangerous to your health, such as viruses and bacteria. When it does its job well, your immune system keeps you from getting sick every time an ill-intentioned germ finds its way into your body.
In some people, however, the immune system has difficulty distinguishing between the good guys (or, at least, the neutral guys) and the bad guys. Like a nervous rookie, it sees danger everywhere and overreacts. A hyperreactive immune system pulls out all the stops for substances that won't do you any actual harm, such as dust, pollen, and animal dander. These innocuous substances are called allergens.
When people who have allergies encounter an allergen, their immune system produces antibodies, called IgE antibodies, that are specific to that substance -- ragweed, for instance, or cat dander.
Thousands of these antibodies bind to the surface of special cells in body tissue called mast cells, which then lie in wait for your next exposure to that specific allergen. While they are waiting, these mast cells absorb many different chemicals from the blood that will aid in the body's defense; they store these chemicals in tiny granules. When you're reexposed to the allergen, the allergen binds to the IgE antibodies on the surface of the mast cells, causing the mast cells to release the chemicals. One of the chemicals, histamine, is probably familiar to you. It is one of the biggest players in the allergic response system and causes many of the reactions, such as runny nose, sneezing, and itchy and watery eyes, that we describe as allergies.
Most anti-allergy medications block the histamine from binding to its receptor and are called antihistamines. The allergic reaction can have both an early and a late phase. Typically the early phase may start within a few minutes of exposure, while the late phase may start several hours after the initial exposure. The early phase is caused by the release of those chemicals stored in the granules in the mast cells. The late phase reaction is caused by other inflammatory cells recruited into the area.
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