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. Bodies of allergic people recognize the foreign substance and parts 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 outdoor agents like pollens and year round indoor agents such as dust and mold. When we first come into contact with these allergens our immune system treats the allergen as an invader and mobilizes an attack. The immune system does this by generating large amounts of a type of a disease fighting protein specific to the particular allergen we are allergic to called antibody. In the case of pollen allergy the antibody is specific for each type of pollen. One antibody may be produced to react against the oak pollen and another against the ragweed pollen. This antibody attaches itself to certain cells in our body. The next time we come into contact with the allergen it attaches to the antibody like a key fitting into a lock and causes the release of some powerful inflammatory chemicals such as histamine. These chemicals move into various parts of our body such as your respiratory system to cause allergy symptoms including runny itchy eyes and sneezing among others. Tobacco smoke is the most common indoor pollutant which is strongly associated with allergic sensitization and other respiratory illnesses. Exposure to smoke enhances the ability of the body to produce the allergy antibody that attaches to allergens called Age. The Age response is a key trigger of allergic reactions. The word allergy is derived from the Greek words alias meaning different or changed and ergo meaning work or action. Allergy roughly refers to an altered reaction. Typically there is a period of sensitization ranging from months to years prior to an allergic reaction. Sometimes it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen but there must have been a prior contact in order for the immune system to be poised to react in this way. Allergies can develop at any age 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 allergy history of parents. If neither parent is allergic the chance that a person will have allergies is about fifteen per cent. If one parent is allergic risk increases to thirty per cent and if both are allergic risk is greater than sixty per cent. It is clear that one must have a genetic tendency and be exposed to an allergen in order to develop an allergy. 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.