An allergy refers to an exaggerated reaction by our immune system in response to bodily contact with certain foreign substances. It is exaggerated because these foreign substances are usually seen by the body as harmless and no response occurs in non-allergic people. Allergic people’s bodies recognize the foreign substance and one part of their immune system are turned on. The substances that are foreign to the body and can cause an allergic reaction in certain people are called ‘allergens’. Examples of allergens include pollens, dust mite, dander, and foods.

When an allergen comes in contact with the body, it causes the immune system to develop an allergic reaction in persons who are allergic to it. So, people can be referred to as allergic if they inappropriately react to allergens that are normally harmless to other people. Allergic disease is more common in highly developed countries in North America and Europe and less common in Third World countries. This suggests that there must be something about modern, urban life that promotes allergy.

Tobacco smoke is the most important indoor pollutant, which is strongly associated with allergic sensitization, asthma, and other respiratory illnesses. Exposure to smoke enhances the ability of the body to produce IgE (the allergy antibody) that attaches to allergens (e.g. pollen, dust mites and dander). The IgE response is a key trigger of allergic reactions.

The term ‘allergy’ was first used by Austrian paediatrician Clemens Pirquet (1874-1929) to refer to the immunity that was beneficial as well as to the harmful hypersensitivity. The word allergy is derived from the Greek words ‘alios’, meaning different or changed and ‘ergos’, meaning work or action. Thus, allergy roughly refers to an ‘altered reaction’. Typically, there is a period of “sensitization” ranging from months to years prior to an allergic reaction.


Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there must have been a prior contact in order for the immune system to be poised to react in this way.

In 1967, the husband and wife team of Kimishige and Teriko jshizaka detected a previously unrecognized type of immunoglobulin in allergic people and called it gamma E globulin or IgE. IgE is an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in large quantities. Normally, this antibody is important in protecting us from parasites, but not from cat dander or other allergens. During the sensitization period, cat dander IgE is overproduced and coats certain potentially explosive cells that contain chemicals.

These cells are capable of causing an allergic reaction on subsequent exposures to the dander. This is because the reaction of the cat dander with the dander IgE irritates the cells and leads to the release of various chemicals, including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes exaggerated and primed to cause an allergic reaction when stimulated by an allergen.

Allergies can develop at any age, possibly even in the womb. They commonly occur in children but may give rise to symptoms for the first time in adulthood. Asthma may persist in adults while nasal allergies tend to decline in old age. Heredity factor also plays a role as the risk of a person developing allergies is related to their parents’ allergy history. If neither parent is allergic, the chance that a person will have allergies is about 15 per cent. If one parent is allergic, risk increases to 30 per cent and if both are allergic, risk is greater than 60 per cent.


It is clear that you must have a genetic tendency and be exposed to an allergen in order to develop an allergy. Additionally, the more intense and repetitive the exposure to an allergen and the earlier in life it occurs, the more likely it is that an allergy will develop. Although people may inherit the tendency to develop allergies, they may never actually have symptoms. Also, people do not necessarily inherit the same allergies or the same diseases as their parents. Some other important influences that may conspire to cause allergic conditions include smoking, pollution, infection, and hormones.

The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Although the various allergic diseases may appear different, they all result from an exaggerated immune response to foreign substances in sensitive people. However, ‘n what may be called the allergy puzzle, it is unclear what determines which substances will trigger a reaction in an allergic person. Additionally, which diseases might develop or how severe the symptoms might be is unknown.

Allergic rhinitis, asthma, allergic eyes, allergic eczema, hives,allergic shock, etc. are common allergic disorders. The most common is allergic rhinitis or hay fever that refers to seasonal nasal symptoms that are due to pollens. Yes sir round or perennial allergic rhinitis is usually due to indoor allergens, such as dust mites, animal dander, molds, or pollens.

Symptoms result From the inflammation of the tissues that line the inside of the nose (mucus lining or membranes) after allergens are inhaled. Adjacent areas, such as the ears, sinuses, and throat can also be involved. The most common symptoms include runny and stuffy nose, sneezing, nasal itching (rubbing), itchy ears and throat, and post nasal drip (throat clearing).


Another disease, asthma is most often, but not always, related to allergies. It is a breathing problem that results from the inflammation and spasm of the lung’s air- passages (bronchial tubes). The inflammation causes a narrowing of the air passages, which limits the flow of air into and out of the lungs. Common symptoms include shortness of breath, wheezing, coughing, and- chest tightness.

Allergic eyes (allergic conjunctivitis) is inflammation of the tissue layers (membranes) that cover the surface of the eyeball and the under surface of the eyelid. The= inflammation occurs as a result of an allergic reaction. Allergic eczema (atopic dermatitis) is an allergic rash that is usually not caused by sic: in contact with an allergen. It is commonly associated with allergic rhinitis or asthma and causes itching, redness, or dryness of the skin.

Hives (urticarial) are skin reactions that appear as itchy swellings and can occur on any part of the body. Hives can be caused by an allergic reaction, such as to a food or medication, but they also may occur in non-allergic people. Typical hive symptoms are raised red welts and intense itching. Allergic shock (anaphylaxis or anaphylactic shock) is a life-threatening allergic reaction that can affect a number of organs at the same time.

It typically occurs when the allergen is eaten (for example, foods) or injected (for example, a bee sting). Some or all of the symptoms which may occur are hives or reddish discoloration of the skin, nasal congestion, swelling of the throat, stomach pain, nausea, vomiting, shortness of breath, wheezing, low blood pressure or shock.


Shock refers to the insufficient circulation of blood to the body’s tissues. Shock is most commonly caused by blood loss or an infection, while allergic shock is caused by dilated and ‘leaky’ blood vessels, which ) result in a drop in blood pressure.