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What is allergy?

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Allergy is a specific immunological reaction to a normally harmless substance, one that does not bother most people. An allergic reaction produces inflammation, a basic response of the body to injury. It is often characterized by redness of the skin, warmth, swelling, and pain. Inflammation results from a complex series of events involving cells and chemicals that are intended to protect the body against invading foreign substances.

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The term allergy was first defined in 1906 by von Pirquet in describing a changed or altered reaction in the body. When an individual develops an unusual response to a substance or condition that is harmless to others, the individual is said to be allergic.

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It is characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response. Common allergic reactions include eczema, hives, hay fever, asthma, food allergies, and reactions to the venom of stinging insects such as wasps and bees.

Allergen : 

Allergen A substance capable of sensitizing the body in such a way that an unusual response occurs, in hypersensitive person. Allergen may be of biologic, chemical or of synthetic origin. Natural allergens are e.g. pollens, danders, dust, etc. Chemical allergens are unknown, but most commonly known is protein or glycoprotein.

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TYPES OF ALLERGY Allergy can be classified into four types on the basis of immune effectors, mediators and cell involved in the reaction. Type I (Immediate) Type II (Cytotoxic) Type III (Immune Complex) Type IV (Cell Mediated or Delayed)




TYPES OF ALLERGEN Allergens can be classified on the basis of types of symptoms, which depend on shock organ affected by the particular allergens and its route of entry into the body. Inhalant Allergens Ingestant Allergens Injectant Allergens Contactant Allergens Infectant Allergens Infestant Allergens

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INHALANT ALLERGENS: Substances that are distributed in the atmosphere and contact the nasal or buccal mucosa during respiration. INGESTANT ALLERGENS: Substances that occur in foodstuffs and are swallowed. INJECTANT ALLERGENS: Substances that may be present in solutions intended for parenteral administration.

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CONTACTANT ALLERGENS: Substances that come into direct contact with the epithelium. INFECTANT ALLERGENS: Metabolic wastes and growth products of pathogenic microorganisms. INFESTANT ALLERGENS: Metabolic wastes and growth products of parasitic microorganisms in or on the body.

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Cause : 

Cause Risk factors for allergy can be placed in two general categories, namely host and environmental factors. Host factors include heredity, sex, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.

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Eye Allergy Causes Ocular (eye) allergies often affect the conjunctiva, this clear layer of skin is the same type of skin that lines the inside surface of the nose. Because these two areas are so similar, the same allergens can trigger the same allergic response in both areas. Common allergens include: Pollen Grass Weeds Dust Pet dander


PEANUTS CAUSE ALLERGY Exposure to peanuts can occur in three ways: Direct contact. The most common cause of peanut allergy is eating peanuts or peanut-containing foods. Sometimes direct skin contact with peanuts can trigger an allergic reaction. Cross-contact. This is the unintended introduction of peanuts into a product. It's generally the result of exposure to peanuts during processing or handling of a food product. Inhalation. An allergic reaction may occur if you inhale dust or aerosols containing peanuts, such as that of peanut flour or peanut oil cooking spray.

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Test for allergies : 

Test for allergies A variety of tests now exist to diagnose allergic conditions; these include testing the skin for responses to known allergens or analyzing the blood for the presence and levels of allergen-specific IgE. Treatments for allergies include allergen avoidance, use of anti-histamines, steroids or other oral medications, immunotherapy to desensitize the response to allergen, and targeted therapy,Base pulse checking.

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When you are exposed to an allergen, one of the symptoms is an increase heart rate. The way to do test is to take your impulse at rest for one minute i:e :BASE PULSE”

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When you eat a food i:e suspect or are exposed to a substance that is suspect, check your pulse again in 15,30 & 60 minutes. If your heart rate accelerates more than 10 beats per minute over your base pulse , it indicates that you may allergic to that particular substance.



Symptoms of allergies to airborne substances include: : 

Symptoms of allergies to airborne substances include: Sneezing, often accompanied by a runny or clogged nose Coughing and postnasal drip   Itching eyes, nose and throat Allergic shiners (dark circles under the eyes caused by increase blood flow near the sinuses)   The “allergic salute” (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose) Watering eyes   Conjunctivitis (an inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes and crusting of the eyelids)

Common symptoms of allergy : 

Common symptoms of allergy

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Normal airway with relaxed muscles. Constricted airway in allergic reaction, with muscles around the airway contracting.





Allergic conjunctivitis : 

Allergic conjunctivitis

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1)Acute response : In the early stages of allergy, a type I hypersensitivity reaction against an allergen, encountered for the first time, causes a response in a type of immune cell called a TH2 lymphocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 (IL-4). These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies.

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Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a particular type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a kind of Fc receptor called FcεRI, the high affinity IgE receptor,) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage are sensitized to the allergen.

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If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation and smooth muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to particular body systems; asthma is localized to the respiratory system and eczema is localized to the dermis

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, Degranulation processes 1- antigen; 2 - IgE antibody; 3 - FcεRI receptor; 4 - preformed mediators (histamine, proteases, chemokines, heparine); 5 - granules; 6 - mast cell; 7 - newly formed mediators (prostaglandins, leukotrienes, thromboxanesPAF)

Mechanism of pollen allergy : 

Mechanism of pollen allergy Pollen grains contain a chemical that binds to the antibodies, Ig E. This antibody is bound to the mast cells in the mucous membrane of the eyes throat, lungs and nose. This stimulates the body to produce histamine and other mediators that cause swelling in the body. The first exposure to the pollen leads to a sensitization and the next time there is exposure to pollen, it causes an allergic reaction. This interaction leads to development of allergic symptoms mentioned above.

Mechanism of Latex Allergy : 

Mechanism of Latex Allergy . Natural rubber latex protein allergy (HBPA) is defined as an IgE-mediated (Type I hypersensitivity) reaction against water-soluble proteins contained in natural rubber products made from the sap of Hevea brasiliensis. Exposure to latex proteins in allergic persons causes the immediate onset of mast cell mediator release. Histamine and other preformed mast cell mediators cause acutely increased vascular permeability and tissue edema. Mast cells also contain mediators that cause delayed inflammatory effects. Immediate hypersensitivity reactions have been elicited by latex protein exposure dissolved from rubber gloves, condoms, barium enema catheters, bladder catheters, balloons, toys and sports

Late-phase response : 

Late-phase response After the chemical mediators of the acute response subside, late phase responses can often occur. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site. The reaction is usually seen 2–24 hours after the original reaction.[36] Cytokines from mast cells may also play a role in the persistence of long-term effects. Late phase responses seen in asthma are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils, and are still dependent on activity of TH2 cells


MECHANISM OF ALLERGY IN ASTHMA When same allergen again come in contact with body, antigen antibody reaction occur which cause mast cell to release mediators that act on nerve ending due to which neuropeptide is release leading in increase production of acetylcholine which cause constriction in bronchial tubules leads to asthma. There is also vasodilation that cause accumulation of mediators resulting in increase amount of mucous in lungs.

Asthma : 


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TREATMENT OF ALLERGY The best way to treat allergy is to avoid the substance which cause it. However , if complete avoidance is not possible , only then is medical treatment recommended and required.

Treatments for allergies : 

Treatments for allergies Treatments for allergies include allergen avoidance, use of anti-histamines, steroids or other oral medications, immunotherapy to desensitize the response to allergen, and targeted therapy


TREATMENT OF ALLERGY There have been enormous improvements in the medical treatments used to treat allergic conditions. With respect to anaphylaxis and hypersensitivity reactions to foods, drugs, and insects and in allergic skin diseases, advances have included the identification of food proteins to which IgE binding is associated with severe reactions and development of low-allergen foods, improvements in skin prick test predictions; evaluation of the atopy patch test; in wasp sting outcomes predictions and a rapidly disintegrating epinephrine tablet, and anti-IL-5 for eosinophilic diseases.


TREATMENT OF ALLERGY Traditionally treatment and management of allergies involved simply avoiding the allergen in question or otherwise reducing exposure. For instance, people with cat allergies were encouraged to avoid them. While avoidance may help to reduce symptoms and avoid life-threatening anaphylaxis, it is difficult to achieve for those with pollen or similar air-borne allergies. Strict avoidance still has a role in management though, and is often used in managing food allergies


PREVENTIVE MEDICINES Certain medicines help to prevent an attack of allergy before it starts. These are available as tablets, syrups and sprays. These have to be started well before the allergy season, and continued till after the season finishes. Although of varying benefit in prevention, these medicines have little use in the treatment of an allergy attack, once it starts


CURATIVE MEDICINES These are commonly known as anti-histamines, as they act against histamine, which is a substance produced in the body, responsible for an allergy episode. These can be started before the season, and are especially effective in controlling an attack of allergy. Available as tablets, syrups or injections, these can be short acting in effect (requiring dosage every few hours), to longer acting, which have to be taken only once or twice daily. The long acting anti-allergics are safer, non-sedating and do not react with other drugs.

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