Allergy is an abnormal reaction to a particle which enters the body from the environment either by inhalation ( breathing), ingestion( eating), injection – (by bites of insects or by injection) and or by contact - the substance comes in contact on the surface of the skin or the mucous membrane of the body of person with allergy, which is usually harmless to other persons. whenever such substance enter the body, body recognizes the sensitive substance and a series of reactions happen either with in few seconds or in minutes to develop the various allergic manifestations