What is allergy?

          Hay fever, rashes on the skin, reactions to certain injections (anaphylactic shock) and some types of asthma are the more common forms of allergy in man. What is an allergy?

          An allergy is an abnormal sensitivity of the body to certain substances especially proteins. In our environment different substances causing allergic reaction are present in countless forms. They may be in pollen or dust that enter the nose or eyes, in the serum of a vaccine or an antibiotic (such as penicillin), or in some food article. Some people are also allergic to feathers and bee stings. There are literally hundreds of allergens. 

          In an allergic reaction the substance causing the reaction is called allergen or antigen, and substances formed within the body during the processes of sensitization are known as antibodies. Though antibodies are one of our main defences against infection but in the event of an allergy they produce unpleasant reactions. The abnormal antibodies on coming in contact with an allergen such as a pollen or fungus, release chemical agents such as histamine, serotonin and other slow reacting substances. The release of these substances produces symptoms of allergy characterized by a running nose, rash and breathing difficulty. Some allergic reactions take several hours to develop while there are others which occur promptly and may cause unconsciousness or even death. They produce fall in blood pressure, difficulty in breathing and a bluish tinge in the skin. 

          It is believed that an allergic substance combines with its antibody and releases a substance called ‘histamine’ in the body. It is this histamine which acts on the blood or other parts and causes allergic symptoms such as sneezing, wheezing, shortness of breath, itching, swelling and redness of the skin. On the basis of this theory antihistamine drugs have been developed for the treatment of several types of allergic reactions. The first antihistamine drug was phyrilamine maleate and today there are wide ranges of similarly acting drugs. They block the action of histamines through their chemical structure.

          Antihistamines can be used to combat hay-fever, asthma, drug rashes, reactions to stings and vaccines. So far, scientists have not succeeded in developing medicines for acute allergic reactions. Development of specific antagonists of chemical mediators of the allergic reactions is required for rational therapy of these diseases. It is important to note that allergic diseases attributable to antigens in the environment are best controlled by avoiding or eliminating the offending substance.

          Medical sciences have yet not been able to explain why certain people are allergic to certain agents, and not others. According to many doctors and scientists heredity has a role in deciding who would be allergic and to what.