Profile of allergy
Some people are very sensitive to certain foods or airborne dust-like protein particles. Such individuals upon exposure to these substances immunologically react with development of physical symptoms which often are associated with itchiness. These symptoms are collectively referred to as allergy. In general, foods cause gastrointestinal (diarrhea, vomiting) and skin symptoms (dermatitis, hives) whereas airborne particles cause respiratory symptoms and sometimes eczema. Thus, an allergy is an abnormal immune reaction to one or more proteins, usually called ‘allergens’ that are harmless to most people. Sources of common allergens that trigger the allergy symptoms include house dust mites, pollens, mould spores, pet dander (skin scales), common foods (e.g. egg, milk, peanuts, shellfish, bird nest soup), drugs (e.g. penicillin, sulphonamides), dyes, cosmetics, perfumes, venom of stinging insects and many other substances.

Some allergies, for example, recurrent rhinitis may be mild in some patients but in other patients the symptoms may be severely debilitating with nasal symptoms all year round. Anaphylaxis is a life threatening condition triggered by stinging insect venom or severe food-allergic reaction. In addition, poorly controlled asthma can be life threatening. In order to manage allergies it is important to identify the causal allergens and manage them as soon as the symptoms first appear. In many cases it is possible to identify the causal allergens even before the symptoms of allergy are present through allergy tests.
Symptoms of allergy vary in complexity, severity and organ manifestation. For the atopic person the effect of allergen exposure can be immediate, with eczema, rhinitis, conjunctivitis, bronchoconstriction, vomiting and diarrhea, and in rare cases anaphylaxis. The symptoms can be simple, such as itchy eyes, or complicated, as in asthma, rhinitis and urticaria. They can be mild or severe. Chronic reactivities can be seen as skin reactions (eczema) and in bronchial asthma an ongoing lung tissue inflammation can be the reason for an asthma attack seen after exposure to the offending allergen. Asthma attacks can also be brought about by other events than allergen-IgE reactions on the mast cell.

In infancy allergies to food, especially egg and milk, seem to be the most common. After the age of 3, most allergic children tolerate these foods, while allergy to inhalant allergens such as dust mite, become predominant. Rhinitis and asthma progressively become dominant allergies in older infants and childhood (see Figure on allergy prevalence). Thus, allergies seen in young infants should be aggressively managed following allergy tests to avoid the progressive development of respiratory allergies.