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WHAT IS ALLERGY?
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An allergy is an inappropriate or exaggerated reaction of the immune system to substances that cause no symptoms in most people. An Allergic individual have an abnormal reaction or increased sensitivity to certain substances and produce symptoms when exposed to these substances, which are harmless to non-allergic people.
The main reason for this is that allergic people make a special type of antibody called Immunoglobulin E (IgE)
to certain environmental substances and which than react to them in a harmful way. These substances are called allergens
and the reaction is called IgE Mediated Allergy.
The reaction between allergens and IgE antibodies causes the release of substances such as histamine, which produce allergic symptoms in the skin, the nose, the eyes, the chest, etc.
The most common allergens are animal dander, pollens, house dust, house dust mites, molds, some drugs and many foodstuffs, especially fish, eggs, milk and nuts. Bee and wasp stings may cause allergic reactions, with fatal results in rare cases. Additionally, feathers, wool, dyes, cosmetics and perfumes may act as allergens.
More on IgE Mediated Allergy
Following exposure to common environmental allergens, the allergic individual produces a special type of antibody, called Immunoglobulin E, or IgE. The healthy individual has a very low level of IgE in the blood, while those with certain allergic conditions such as hay fever, allergic asthma and some forms of eczema have high IgE levels. People with eczema have especially high blood levels of IgE.
In the human body, certain cells called mast cells and basophils are involved in allergic reactions. IgE, produced as a result of repeated allergenic stimulation, attaches to the surface of these cells and subsequent binding of the allergen punctures the cell wall, leading to the release of different substances.
These substances cause a build-up of fluid in the tissue, and contraction of the smooth muscles. Depending on the route of entry of the allergen and where the reaction takes place, different symptoms will occur. If the reaction takes place in the nose and eyes, hay fever will result - while asthma is the result if the chest is affected. Eczema appears when the skin is affected.
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Allergy Screen - Basic Molds |
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 Cladosporium herbarum
Aspergillus fumigatus
Mucor racemosus
Candida albicans
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Alternaria tenuis
Helminthosporium spp.
Fusarium moniliforme
Pullularia pullulans
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Phoma betae
Epicoccum purpurascens
Stemphylium solani
Hormodendrum hordei
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The Mechanism of an Allergic Reaction
There are three stages to the allergic response: In the first stage, the immune system encounters the foreign substance and identifies it as an invader. It then primes the immune system to recognize this invader as an enemy that needs to be destroyed in future encounters. This stage is known as sensitization. The subsequent stages are mast cell activation, and prolonged immune activation.
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STAGE 1- SENSITIZATION
The first time an allergen meets the immune system, no allergic reaction occurs. Instead, the immune system prepares itself for future encounters with the allergen. Scavenger cells called macrophages surround and break up the invading allergen. The macrophages then display the allergen fragments on their cell walls to specialized white blood cells, called T lymphocytes, which are the main orchestraters of the body's immune reaction. The T cells secrete a signaling chemical called interleukin-4, which activates other white blood cells known as B lymphocytes. These cells secrete antibodies specific for that particular allergen. These antibodies, called immunoglobulin E (IgE) receptors, are attached to cells in the immune system, called mast cells and basophils. Individuals prone to allergies are known to have abnormally high levels of IgE antibodies.
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STAGE 2- MAST CELL ACTIVATION
Stage 2, or mast cell activation, represents a later encounter between the allergen and the immune system and usually occurs within minutes after the second exposure to an allergen. IgE antibodies on mast cells, constructed during the sensitization phase, recognize the allergen and bind to the invader. Once the allergen is bound to the receptor, granules in the mast cells release their contents.
These contents, or mediators, are substances such as histamine, platelet-activating factor, prostaglandins, and leukotrienes. Mediators are what actually trigger the allergy attack. Histamine stimulates mucus production and causes redness, swelling, and inflammation. Prostaglandins constrict airways and enlarge blood vessels.
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STAGE 3- LATE PHASE INFLAMMATORY RESPONSE
In Stage 3 tissue mast cells and neighboring cells produce chemical messengers that signal circulating basophils, eosinophils, and other cells to migrate into that tissue, to help fight the foreign material. These recruited immune cells secrete chemicals of their own that sustain inflammation, cause tissue damage, and recruit yet more immune cells. This phase occurs several hours after exposure and can last for hours and even days.
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COMMON ALLERGIES
Allergic reactions or diseases may involve any part of the body; the most frequently involved are the nose and chest with resultant symptoms of hay fever, rhinitis or asthma, respectively. The skin and eyes also commonly show allergic symptoms. Anaphylactic shock is a severe allergy, which affects many organs at the same time causing a rapid decrease in blood pressure, fainting and, occasionally, death. Such a reaction, though, is rare.
Hay Fever
If you suffer from hay fever, the pollens of grasses, weeds and trees are the main causes of this type of allergy, although mold spores can also cause the symptoms.
The lining of the nose becomes swollen and exudes a runny discharge. Spells of sneezing and itchiness of the throat and palate also occur and the eyes may be similarly affected.
Depending on where you live and the pollinating periods, attacks may occur in spring, summer or autumn. Contact lense wearing time may decrease due these symptoms
In perennial allergic rhinitis, the symptoms are similar to hay fever but appear all the year round. This condition is caused by non-seasonal allergens such as house dust components and certain molds.
Conjunctivitis
You are more likely to suffer from this allergic condition of the eyes as an adult. Allergic conjunctivitis is often associated with allergic rhinitis. A general complaint is of itchiness of the eyes, which are rubbed frequently.
Asthma If you have asthma, you can suffer from attacks that obstruct the flow of air to the lungs. Breathing becomes difficult and forced breathing becomes necessary. A wheezing sound can appear, due to the rush of air through your narrowed airways. At the same time, a troublesome cough can develop. Asthma may begin at any age and, if neglected, tends to recur and become chronic.
Eczema
If you suffer from eczema, your skin can become irritated and develop rashes that can be either wet or dry and occasionally chapped. The reactions are often accompanied by severe itching. The cause is often not clear, but is frequently seen in children of families with a history of allergic diseases. The eczema may start during the first year of life, on the face. Later, it is often seen on the inside of the elbows and backs of knees, on the neck, on the ankles, on the wrists and on the back of the hands. It is possible for eczema to become secondarily infected with skin bacteria, especially if there is much broken skin due to scratching.
Urticaria, Hives (Nettlerash)
This reaction appears very suddenly. Your skin becomes warm, reddish and itching. The symptoms may last either for a couple of hours or up to a whole day. Blotches may appear as raised wheals and vary in size from smaller than a mosquito bite to several inches in diameter. In 95% of hives, the cause is unknown.
Contact Dermatitis
With contact dermatitis, your symptoms will be similar to those of the eczema previously described, but this reaction is of another type. The cause is direct contact with different substances, such as: nickel (in coins, stainless steel, clasps, jewelry) rubber products (in gloves, boots, waistbands); chromium (in cement, leather)
latex, preservatives (in creams, ointments and cosmetics).
This condition, unlike those listed above, is not due to the production of IgE antibodies, but is due to a different kind of immune reaction. It is usually due to increased sensitivity to a substance that a particular body part contacts.
Food Allergy
The stomach and the digestive system are also frequent targets for allergic disease. Your symptoms are caused by allergy to foods, which can result in vomiting, stomach pains, diarrhea or constipation. Frequently, eczema and hives may be produced after ingesting food to which you are allergic. Food allergy may also trigger asthmatic attacks and, rarely, generalized anaphylaxis. Food anaphylaxis is most commonly seen with ingestion of nuts and iodinated shellfish (lobster, shrimp).
Insect Allergy
Severe allergic reactions to bee and wasp stings are not uncommon. More people die annually in the United States from insect sting allergy than die from snakebite. The local toxic reaction and discomfort that usually occurs following an insect sting is not generally considered to be allergic.
IgE mediated (allergic) reactions induce symptoms such as nettlerash (urticaria, hives), running nose and eyes, swelling of the throat, attacks of asthma and, in severe cases, fainting.
Swelling of an entire extremity is called a "large local reaction." Although indicative of hypersensitivity, this type of reaction does not, generally, proceed to anaphylaxis with future stings.
If you have had a severe insect sting or allergic reaction, your clinician may provide you with an adrenaline containing kit for use if you are stung. Should you be highly sensitive to bee or wasp stings, you may become unconscious within a short space of time. Immediate action should be taken to get you expert medical treatment, preferably at the nearest hospital.
Occupational Allergy
The term occupational allergy is generally used to describe episodes of allergic reactions occurring after working with industrial dusts, vapors, gases or fumes. Furthermore, substances like nickel (in coins), chromium (in cement), rubber, different dyes, formaldehyde and glues may result in eczema that occurs at the site of contact with the skin. Inhalants such as grain dust may affect farmers.
The degree of eczema depends on the length of exposure and sensitivity to the substance. Symptoms may show within some weeks - but it can often take months, years, sometimes decades, before an eczema develops. Any part of the skin may become affected, but the most frequent sites are the hands, arms and the face, because these tend to be the least protected parts of the body. Occupational allergy may also present with pulmonary or upper respiratory treatments. Workers will often get better over the weekend, on business trips, or vacation and symptoms will often recur after return to the same work environment.
Who Becomes Allergic?
Anyone can develop an allergy, but the probability is increased if one or both parents suffer from some kind of allergic condition. Indeed, the presence of another allergic individual in the family is the strongest factor for predicting allergy in a child. It must be noted, though, that even when both parents are affected, a child may not be. Conversely, allergic children are born to normal parents and in such cases other factors, such as infection, may be responsible for the development of the allergy. Repeated exposure to a substance is required before the body can recognize it as foreign and mount an allergic response.
DIAGNOSIS
It is essential for successful treatment that the allergens responsible for the symptoms are accurately identified. There are different ways to arrive at a diagnosis. The case history is extremely important in all allergy investigations. Based on what the patient tells about his/her symptoms, the doctor decides what tests, if any, should be carried out.
Laboratory Tests
IgE plays an important role in allergic rhinitis, allergic asthma and in some forms of eczema. Detecting and accurately measuring the amount of IgE may be of great importance when diagnosing allergies.
Because of the limitations and disadvantages associated with skin and provocation tests, there has been a need for more convenient and reliable methods. Today, there are laboratory tests available that accurately measure IgE, and a small blood sample is sufficient for allergy testing. These tests measure either the total amount of IgE in the blood, which indicates if your symptoms are of allergic origin or specific IgE, which tells the doctor which allergens are causing the trouble. Another allergy blood test is called RAST (radioimmunoabsorbent test). These blood tests are significant primarily if the identified substances cause patient symptoms. RAST is especially helpful in very young children.
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 Allergies - The Facts
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