How allergies affect the body
A person can be allergic only to something to which he or she has already been exposed. In other words, an allergic response occurs after an initial exposure to a substance to which the person’s immune system is sensitive. It is reexposure to the substance that produces the allergic reaction.
The first time an allergen enters the body of a person who is likely to develop allergies, a certain type of allergen-specific antibody is produced. This antibody, called immunoglobulin E (IgE), travels to mast cells in many areas of the body. Mast cells are commonly found in the nose, eyes, lungs, and gastrointestinal tract. IgE antibodies attach themselves to the surfaces of these mast cells. Each IgE antibody is waiting for an invasion by a particular allergen.
Let’s say that a person is predisposed to developing an allergy to cat dander. The IgE antibody for that allergen can be found on the surface of that person’s mast cells. He or she might develop an allergy to cat dander only. This means that the person’s allergies will not be triggered by dog or horse allergens, unless, of course, those allergen-specific IgE antibodies are present as well.
Therefore, the IgE antibodies to cat dander have “set up camp” on the mast cells. The very next time that the person comes into contact with cat dander, this allergen will enter the body. The waiting IgE antibodies will capture these cat dander allergens. Once this happens, chemicals such as histamine are released from the mast cells. These chemicals, often called mediators, are responsible for producing the symptoms of an allergic reaction, such as sneezing and coughing. As the person continues to be exposed to the cat dander allergen, the reaction continues. Already inflamed tissues might grow more inflamed as these chemicals draw other swollen cells to the area.
The reaction that the person has depends upon the location of the mast cells to which the IgE antibodies have attached. For example, if an allergen such as pollen touches the lining of the nose, as is common in allergic rhinitis (hay fever), the mucous membranes that line the nose will become inflamed and congested. The person will experience a dripping nose and watery, itchy eyes. If the person continues to be exposed to the allergen that triggered the reaction, the symptoms will continue the same way.
A person with a very different trigger — for example, a food that produces eczema — will experience symptoms that affect the skin. For 80% of those with eczema, this condition — itchy, reddening, flaking, and peeling skin — begins in childhood. Another skin-specific allergic reaction can occur from an infection, eating a certain food, or taking a certain medication.
Hives can cover the skin with small or large clusters of itchy, red bumps. Children experience allergic reactions to food more frequently than adults do. Over time, a child can become less sensitive to foods that were once allergy triggers.
Food can also be a trigger for anaphylaxis. A person who is in immediate danger from this severe allergic reaction should be given an injection of epinephrine (adrenaline) as soon as possible. Otherwise, the episode could be fatal. Epinephrine is a body chemical that is produced naturally by the adrenal glands. Used in injections, a synthetic form of the chemical fights allergic reactions in several ways. Epinephrine opens constricted air passages, constricts dilated blood vessels, elevates low blood pressure, and halts the swelling that is common with hives.
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