An allergy, as previously explained, is an abnormality of the immune system. The immune system reacts in an uncharacteristic way against an inoffensive “foreign” substance which leads to tissue injury and subsequent symptoms of allergy.
Allergy and Atopy
An allergy is genetically inherited. Allergic parents will give rise to allergic children. Let us understand at this point that if the parents are allergic, it is not obligatory for the children to be allergic, although they are “atopic.” Atopy refers to the propensity to develop an allergy. That is, an atopic individual is the one who has the genetic defect(s) that make him/her predisposed to develop allergy.
Presence of Allergen is Important
If the atopic individual does not come in contact with the allergen during his/her lifetime, he/she will never develop an allergy! It is also known that if one of the parents suffers from, for example, a food allergy (peanuts!), it is highly possible that the child may develop a different kind of allergy, say, hay fever. Now if the offending allergen is ragweed pollen and the child emigrates to a region in the world where there is no ragweed pollen, then the child will never develop an allergy against ragweed pollen!
But the child is atopic (genetic propensity to develop an allergy) and will develop an allergy if he/she ever comes in contact with the allergen. That is, although the child bears the defective genes making him/her inclined towards developing an allergy, the presence or absence of the allergen in the environment will finally determine whether an allergy develops or not.
Environmental Factors Also Play a Role
Furthermore, there are many environmental factors that also affect the development of an allergy. It is also known that a particular allergen might play havoc in one part of the world but might fail to show similar kinds of effects in another. Also racial characteristics determine response given by an individual against a particular allergen. For example, inner-city African American children are more prone to developing hay fever than their Caucasian or Hispanic counterparts.
Although a few genes responsible for causing many different types of allergy have been detected, we are still a long way from revealing all the possible candidate genes. And even if we are successful in discovering every gene which has something to do with the development of an allergy, we will, probably, never be able to tell for sure whether the presence of a particular gene makes the individual allergic.
