What is Allergy?

What is Allergy?

Allergy is the extreme sensitivity of an individual to certain substances in the air or to foods, which are ­harmless to most other individuals. For example, when a room is dusted an allergic individual may get an asthmatic attack or bouts of sneezing. When an allergic person takes a particular food or medicine, he may break out with a skin rash. Nothing may happen to a person who does not have an allergic tendency.

Man and other living beings have to depend on the environment to survive – to receive oxygen for tissue oxygenation and for food for tissue nourishment. However, in addition to the air we breathe, a number of unwanted items enter – dusts, pollens, fungi, mites, etc. Similarly, foods have to enter from the external world, since man cannot manufacture his own food like plants. Many foods may not agree with some individuals – “One man’s food may be another man’s poison”. Also substances in contact with the skin and injected into the skin like insect stings and injected drugs can cause allergic reactions.

Man in his environment

When the body is repeatedly exposed to these foreign substances (called allergens or antigens) the body develops specific fighting bodies (antibodies). Every time a foreign substance enters the body, the antibodies fight it by a reaction known as antigen antibody reaction. Basically, this is a protective reaction. In case of bacterial and viral infections it stimulates the body to form antibodies, which develop immunity to disease e.g. mumps, measles, etc.

In some individuals however, the antigen antibody reaction takes a violent and exaggerated form. This is an allergic reaction and is harmful to the individual. Certain violent allergy reactions can be fatal, like injections of Penicillin, stings of bees, wasps, scorpions. Repeatedly occuring allergen antibody reactions can cause increasing, irreversible, permanent tissue changes in the target organs-the organs most commonly affected by allergy – the lungs, the nose and the skin.

Allergic reactions in the body manifest as allergic disease. This is explained later.

Allergic diseases

The term allergy encompasses the clinical characteristics of type 1 hypersensitivity reaction, which includes asthma, allergic rhinitis (hay fever) and urticaria and other diseases which can have an allergic background e.g. – Food allergy, migraine etc..

Various organs in the body (known as the target organs) can be affected by allergy and give rise to specific symptoms and diseases. The lungs, nose and skin are the main target organs where the allergic reaction usually occurs.

Lung allergy is characterized by sudden cough, sputum accumulation in the chest, wheezing and difficulty in breathing – allergic bronchitis or asthma.

Nasal allergy is characterized by sudden bouts of sneezing and watery nasal discharge often with itching and blocking of the nose – allergic rhinitis. Long-standing nasal allergy can lead to formation of nasal polyps with severe nasal obstruction. Bronchial asthma develops in 15% of patients suffering from allergic rhinitis.       .

Skin allergy is characterized by skin rashes with itching.

Other organs of the body may be similarly affected. In allergy there is fluid logging in the tissues.

When this occurs in the brain and nerves, mental dullness, tiredness and migraine headaches can occur. In the gastro intestinal tract, abdominal pain, loose stools may occur. When the eyes are affected, itching and swelling can occur. When the inner ear is affected, attacks of vertigo or a sense of imbalance is often present.

Factors that make an Allergy worse: :

These are known as “Trigger Factors” since they activate the trigger of the allergen-loaded gun to “fire”.

Respiratory infections,

Exercise Emotional stress,

Change in humidity Weather change,

Cigarette smoke,

Exposure to street dust,

Perfumes,

Incense smoke,

Mosquito coils,

Insecticide  sprays,

Fresh-up sprays,

Smoke from factories,

Automobile exhaust  etc.

Mechanism of Allergy

The allergic tendency (tendency to over react to a foreign substance) is often inherited from parents. Such individuals when subject to allergens e.g. house dust, pollen, certain foods etc., which they may be sensitive to give the “allergic reaction.”

The “March” concept – The allergic march / Atopic march describes the progression of one clinical manifestation of allergy to the next, throughout a person’s life time. Allergic responses of the body take place mainly in the large target organs – Nose, Chest and Skin. It has been found that while the affection starts with one organ, it can “march” ahead to involve other target organs. For instance, 15% of patients with Allergic rhinitis eventually go on to develop asthma. After some months or years later, a skin allergy or food allergy may develop.

The “Total allergic load” concept.  Allergy is usually caused by a number of allergens in differing proportions. Allergic symptoms like sneezing, wheezing, urticaria are precipitated when the patient is exposed to a large dose of a single allergen, or more commonly, to small doses of a number of allergens. The moment the effects of several allergens build up to a certain upper limit, (threshold level), allergic symptoms are precipitated – the symptoms being that of the target organ affected in a particular individual – Lung, Nose or Skin. Physical factors like change in climate or humidity may increase the chance of allergic attacks by acting as triggering factors.

The allergy response is basically an inflammatory response and makes the target organ excessively responsive and sensitive – resulting in chronic mucus secretion, tissue damage etc. Repeated exposure to an allergen induces a chronic inflammation and ultimately progressive irreversible changes in the target organ – Lung, Nose or Skin.

Who should have an allergy test performed?

Individuals suffering from classical allergic disease like asthma, allergic rhinitis and dermatoses, should most certainly have an allergy test performed.

It is common experience that after taking certain foods, we feel unwell and tired. Headaches, gaseous distension in the abdomen, abdominal cramps, a feeling of fullness and bloating of the abdomen after meals, diarrhoea follow ingestion of certain foods.

An always tired and weak feeling, mental dullness, feeling sleepy all the time even after a complete night’s sleep, low grade fever, muscle and joint pains, body aches, sore throat, swollen glands, unexplained headaches and, sensitivity to extremes of temperature has been blamed on allergy to some substance in the environment “that does not agree” with the individual.

Again vague abdominal pains, recurrent colds and nagging cough not responding to routine treatment, constant fatigue, tension, swelling of eyelids and face, blocking of the nose, diminished sense of smell, mild transient giddiness – in fact many symptoms labeled as ‘vague complaints’ by doctors can eventually be traced to a food or dust allergy. When the body’s immunity is compromised, the body’s resistance to infection is lowered and we are vulnerable to virus infection. Even viral infections occurring in childhood and lying dormant for several years are reactivated, when excess work and tension of modern existence sap up body resources. We fall victim to what is known as CFIDS (Chronic Fatigue Immune Dysfunction Syndrome).

Clinical approach to diagnosis of allergy

The Nose and Throat are the portal of entry of most allergens, both inhalants and foods.

A thorough Nose and Throat examination is therefore mandatory to exclude the conditions which aggravate the allergy. It is essential to exclude sinus infection, infected tonsils and abnormalities of air entry through the nose due to deviated nasal septum, adenoids, nasal polyps etc. The following page gives details on these conditions.  Not paying attention to these would render the treatment of allergy incomplete.

Common disease conditions affecting the Nose and Sinuses


Special investigations often required :

1). C.T. Scans of nose and the paranasal of sinuses.

2). A chest examination and chest specialist consultation may also be required.

Chest X-rays to exclude diseases like tuberculosis.

Lung function tests.

Sputum examination to exclude diseases like tuberculosis.

3). Blood examination to exclude eosinophilia

Stool examination to exclude worms and parasites;

Nasal discharge examination to note the  presence of eosinophils may be required.