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 Understanding about
 Allergies
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What Are Allergies?
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Types of Allergies
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   What Are Allergies?/ โรคภูมิแพ้      
Allergies are the immune system's incorrect response to a foreign substance. Exposure to what is normally a harmless substance, such as pollen, causes the immune system to react as if the substance is harmful. Substances that cause allergies are called allergens.

When you come into contact with an allergen, you may experience a number of allergic symptoms, including itchy, watery nose and eyes, asthma, wheezing and coughing or hives.

What Is An Allergic Response?

An allergic reaction is the result of how three factors interact with the body:

  • The allergen. Allergens include pollen, mold, dust mites, certain foods, latex, animal dander and others.
  • Mast cells. Though mast cells, a type of white cell, are found throughout the body, most reside in connective tissues such as those of the skin, tongue, the lining of the nose and intestinal tract, the lungs, and upper airways.
  • Immunoglobulin E (IgE). This is an allergic antibody, a type of protein made by the immune system to recognize and fight specific body "invaders." IgE coats the surface of the mast cells in tissues.

The first time an allergy-prone person is exposed to an allergen (such as pollen), large amounts of the corresponding IgE antibody (for example, pollen IgE antibodies) are produced.

During the next exposure, these antibodies activate, causing the mast cells to release inflammatory chemicals that lead to swelling of tissues, itching, engorgement of blood vessels, increased secretions and tightening of muscles that surround the airways (bronchospasm). Some of these chemicals attract other white blood cells known as eosinophils. The eosinophils add more inflammatory chemicals.

If the allergen is in the air, the allergic reaction will occur in the eyes, nose, and lungs. If the allergen is ingested, the allergic reaction will occur in the mouth, stomach, and intestines.

Sometimes enough inflammatory chemicals are released to cause a reaction throughout the body, such as hives, decreased blood pressure, shock or loss of consciousness. This severe type of reaction is called anaphylaxis and may be life-threatening.

What Are The Symptoms Of Allergies?

Allergy symptoms can be categorized as mild, moderate, or severe (anaphylactic).

Mild reactions include local symptoms (affecting a specific area of the body) such as a rash or hives, 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 (anaphylaxis) is a rare, life-threatening emergency in which the body's response to the allergen is sudden and affects the whole body (systemic). It may begin with acute itching of the eyes or face and within minutes progress to more serious symptoms, including varying degrees of swelling as in hives or angioedema (if the airways or throat are involved in the swelling, this could result in difficulty swallowing and breathing), abdominal pain, cramps, vomiting, and diarrhea.

Mental confusion or dizziness may also be symptoms, since anaphylaxis causes a quick drop in blood pressure.

What Are The Common Types Of Allergies?

People can be allergic to a variety of substances, the most common of which are pollen and dust mites.

Pollen: Allergic rhinitis, or hay fever, is the allergic response to pollen. It causes inflammation and swelling of the lining of the nose, as well as the lining of the eyes and eyelids (conjunctiva).

  • Symptoms include sneezing, congestion and itchy, watery eyes.
  • Treatments include over-the-counter and prescription antihistamines, nasal steroids, and nasal cromolyn. Prevent pollen exposure by staying indoors when pollen counts are high, closing windows and using air conditioning.

Dust mites: These are microscopic organisms that live in dust. House dust is a mixture of potentially allergenic materials including fibers from different fabrics, dander from animals, bacteria, mold or fungus spores, food particles, bits of plants or other allergens.

  • Symptoms are similar to those for pollen allergy and can also produce symptoms of asthma such as wheezing and coughing.
  • Treatments include medications such as antihistamines or decongestants. Immunotherapy may be recommended for people whose symptoms are chronic.

Molds: These are parasitic, microscopic fungi (like Penicillium) with spores that float in the air like pollen. Mold is a common trigger for allergies and can be found in damp areas such as the basement or bathroom, as well as in the outdoor environment in grass, leaf piles, hay, mulch or under mushrooms. In some people, symptoms of mold allergy may be brought on or made worse by eating certain foods, such as cheese processed with fungi.

  • Symptoms include sneezing, congestion, itchy, watery eyes, runny nose and coughing.
  • Treatment with antihistamines or corticosteroids is usually helpful, but avoiding these substances is important also.

Animal dander: Proteins secreted by oil glands in an animal's skin, as well as the proteins present in an animal's saliva, cause allergic reactions in some people. Allergies to animals can take two or more years to develop and symptoms may not subside until months after ending contact with the animal.

  • Symptoms include sneezing, congestion and itchy, watery eyes.
  • Treatments include avoiding exposure to the animals causing your allergies if possible. Medications such as antihistamines or decongestants may be helpful, or immunotherapy may be recommended if your symptoms are chronic.

What Other Allergies Are There?

Latex: Latex allergy develops after some sensitizing contact with latex. Rubber gloves are the main source of allergic reactions. A component of the latex substance itself is an allergen for many people. The latex glove powder is an airborne allergen, which causes upper airway allergic reactions in some people, as well as worsening asthma.

  • Symptoms include skin rash, hives, eye tearing and irritation, wheezing and itching of the skin. Allergic reactions to latex can range from skin redness and itching, to much more serious symptoms such as difficulty breathing, hives, or acute (sudden-onset) gastrointestinal problems.
  • Treatments include removal of the latex product and drugs according to the type of symptoms developing. If you have latex allergy, it is important for you to wear a MedicAlert bracelet and carry an emergency epinephrine kit at all times. There is no cure for latex allergy, so the best treatment is prevention.

Foods: Food allergies develop when there is an IgE antibody to a specific food. An allergic reaction occurs within minutes of eating the food and symptoms can be severe. Milk, fish and shellfish, nuts, peanuts, wheat and eggs are the most common foods that cause allergies. Non-allergic food intolerance is more common than true food allergy.

  • Symptoms include asthma (wheezing and coughing), hives, runny nose, vomiting, diarrhea, swelling in the area around the mouth.
  • The best treatment is to avoid the foods that cause allergy symptoms. For rashes, skin creams may ease discomfort, while antihistamines will help reduce itching, congestion, and other symptoms. For more serious reactions, corticosteroids such as prednisone will help to reduce swelling. In life-threatening situations, an epinephrine (adrenaline) injection immediately begins reversing symptoms and is the only effective treatment option.

Insect venom (stings): Everyone who gets stung by an insect will have pain, swelling, and redness around the sting site. However, some people are allergic to stings and have severe or even life-threatening reactions.

  • Symptoms include difficulty breathing; hives that appear as a red, itchy rash that spreads to areas other than the immediate area stung; swelling of the face, throat or mouth tissue; wheezing or difficulty swallowing; restlessness and anxiety; rapid pulse; dizziness or a sharp drop in blood pressure.
  • You may take an oral antihistamine, like Benadryl, to reduce itching, swelling, and hives. To relieve pain, take aspirin or an aspirin substitute. An allergic reaction is treated with epinephrine (adrenaline), either self-injected or administered by a doctor. Usually this injection will stop the development of severe allergic reaction.

What Is Allergic Rhinitis?

Nasal allergy symptoms and hay fever are referred to as "allergic rhinitis." Seasonal allergic rhinitis describes nasal allergies that change with the seasons due to plant pollens (from trees, grasses, or weeds).

Seasonal symptoms arise during the pollinating seasons for particular plants. Because you can be allergic to more than one thing, your symptoms may get worse at different times throughout the year or they may appear constant (perennial).

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. If a child develops an allergy it is very likely that at least one of his or her parents has allergies.

Being exposed to allergens at certain times when the body's defenses are low or weak, such as after a viral infection or during pregnancy, may also contribute to the development of allergies.

How Common Are Allergies?

Allergic disorders affect more than 20 percent of adults and children (40 to 50 million people) and are the sixth leading cause of chronic illness in the United States, according to the American Academy of Allergy, Asthma and Immunology.

How Are Allergies Diagnosed?

If you think you have allergies, don't wait to see if your symptoms go away. When your symptoms last longer than a week or two and tend to recur, make an appointment with your doctor so a complete medical evaluation can be performed.

An allergy skin test, also called a scratch test, may be used to identify the substances that are causing your allergy symptoms. It is performed by scratching an extract of an allergen placed on your skin and then evaluating the skin's reaction.

If a skin test cannot be performed, a radioallergosorbent blood test (RAST) may be taken, although its results are not as accurate as a skin test. This test evaluates the number of antibodies produced by the immune system. Elevated levels of certain antibodies can identify particular allergies.

How Are Allergies Treated?

Medications such as antihistamines, decongestants or a combination of both of these medications can be taken over-the-counter or by prescription to treat allergy symptoms. Nasal sprays such as topical nasal steroids and cromolyn sodium can also be used to treat allergy symptoms. Immunotherapy, or allergy shots, is recommended for relief needed over a long period of time.

Can Allergies Be Prevented?

Allergies cannot be prevented, but they can be treated and controlled. Making changes in your environment can greatly limit your exposure to certain allergens and reduce your symptoms

 

   Types of Allergies   อาการภูมิแพ้มีสาเหตุได้จาก      
Not all allergies are created equal. Food allergies can cause very different symptoms than pollen allergies. But they all have one thing in common -- they're a defensive reaction by your body's immune system to a substance that is usually harmless.

This section provides information on the various types of allergies and allergy-related conditions. Each article describes the recommended treatment for that condition. This section also contains important information on how to handle life-threatening allergic reactions, called anaphylactic reactions.

Here's a list of the complete contents of this section:

 Anaphylaxis
 Asthma
 Conjunctivitis
 Drug Allergies
 Food Allergies
 Hay Fever (Rhinitis)
 Insect Stings
 Latex Allergy
 Otitis Media 
 Sinusitis
 Hives (Urticaria and angioedema)

Copyright ©2000 content, The Cleveland Clinic. The information provided by The Cleveland Clinic is not intended to replace the medical advice of your doctor or health-care provider. Please consult your health-care provider for advice about a specific medical condition. For additional health information, please contact the Health Information Center at The Cleveland Clinic, (216) 444-3771 or toll-free (800) 223-2273, Ext. 43771.

May 2001, Medically Reviewed by Dominique S. Walton, MD, MBA, WebMD.