Allergies are an abnormal response of the immune system. People who have allergies have an immune system that reacts to a usually harmless substance in the environment. This substance (pollen, mold, animal dander, etc.) is called an allergen.
Allergies are a very common problem, affecting at least 2 out of every 10 Americans.
What Happens During an Allergic Reaction?
When a person is exposed to an allergen, a series of events takes place:
- The body starts to produce a specific type of antibody, called IgE, to bind the allergen.
- The antibodies attach to a form of blood cell called a mast cell. Mast cells can be found in the airways, in the GI tract, and elsewhere. The presence of mast cells in the airways and GI tract makes these areas more susceptible to allergen exposure.
- The allergens bind to the IgE, which is attached to the mast cell. This triggers a reaction that allows the mast cells to release a variety of chemicals including histamine, which causes most of the symptoms of an allergy, including itchiness or runny nose.
If the allergen is in the air, the allergic reaction will likely occur in the eyes, nose and lungs. If the allergen is ingested, the allergic reaction often occurs in the mouth, stomach, and intestines. Sometimes enough chemicals are released from the mast cells to cause a reaction throughout the body, such as hives, decreased blood pressure, shock, or loss of consciousness.
What Are the Symptoms of Allergies?
Allergy symptoms can be categorized as mild, moderate, or severe (anaphylactic).
- Mild reactions include those symptoms that affect a specific area of the body such as a rash, itchy, watery eyes, and some congestion. Mild reactions do not spread to other parts of the body.
- Moderate reactions include symptoms that spread to other parts of the body. These may include itchiness or difficulty breathing.
- A severe reaction, called anaphylaxis, is a rare, life-threatening emergency in which the response to the allergen is intense and affects the whole body. It may begin with the sudden onset of itching of the eyes or face and progress within minutes to more serious symptoms, including abdominal pain, cramps, vomiting, and diarrhea, as well as varying degrees of swellings that can make breathing and swallowing difficult. Mental confusion or dizziness may also be symptoms, since anaphylaxis causes a quick drop in blood pressure.
Does Everyone Have Allergies?
No. Most allergies are inherited, which means they are passed on to children by their parents. People inherit a tendency to be allergic, although not to any specific allergen. When one parent is allergic, their child has a 50% chance of having allergies. That risk jumps to 75% if both parents have allergies.
What Causes Allergies?
Almost anything can trigger an allergic reaction.
- The body’s immune system has a patrol of white blood cells, which produce antibodies.
- When the body is exposed to an antigen, a complex set of reactions begins.
- The white blood cells produce an antibody specific to that antigen. This is called “sensitization.”
- The job of the antibodies is to detect and destroy substances that cause disease and sickness. In allergic reactions, the antibody is called immunoglobulin E, or IgE.
- This antibody promotes production and release of chemicals and hormones called “mediators.”
- Histamine is one well-known mediator.
- Mediators have effects on local tissue and organs in addition to activating more white blood cell defenders. It is these effects that cause the symptoms of the reaction.
- If the release of the mediators is sudden or extensive, the allergic reaction may also be sudden and severe.
- Your allergic reactions are unique to you. For example, your body may have learned to be allergic to poison ivy from repeated exposure.
- Most people are aware of their particular allergy triggers and reactions. Certain foods, vaccines and medications, latex rubber, aspirin, shellfish, dust, pollen, mold, animal dander, and poison ivy are famous allergens.
- Bee stings, fire ant stings, penicillin, and peanuts are known for causing dramatic reactions that can be serious and involve the whole body.
- Minor injuries, hot or cold temperatures, exercise, or even emotions may be triggers.
- Often, the specific allergen cannot be identified unless you have had a similar reaction in the past.
- Allergies and the tendency to have allergic reactions run in some families. You may have allergies even if they do not run in your family.
- Many people who have one trigger tend to have other triggers as well.
- People with certain medical conditions are more likely to have allergic reactions.
- Severe allergic reaction in the past
- Lung conditions that affect breathing, such as chronic obstructive pulmonary disease (COPD)
- Nasal polyps
- Frequent infections of the nasal sinuses, ears, or respiratory tract
- Sensitive skin
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