Atopy versus allergy

Very often allergy sufferers are said to be atopic. So what does this mean? Is it the same thing as allergy? The answer is not simply yes or no.

Atopy is the genetic predisposition of an individual to produce high quantities of IgE in response to allergens in the environment (pollens, house dust mites, moulds, cat dander, foods etc). Heredity is very important in atopy i.e., you inherit this predisposition to produce IgE from your mother, your father, or both. Thus, atopy represents the background for sensitisation: only atopic people (those with genetic predisposition) develop sensitisation to one or more allergens. Atopy is silent; atopic people do not necessarily display symptoms when they come across allergens. A person might suspect that he or she could be atopic if they have relatives who suffer from allergies.  The only way to identify atopy is through allergy tests which measure IgE for various allergens.  So atopy is a condition for the development of allergy but is not itself allergy!

Allergy, in medical terms, means that the person develops symptoms upon contact with allergens to which he/she is sensitised.

So you need to be atopic to become allergic but if you are atopic you will not necessarily progress to an allergic state (not all atopic people start developing allergy symptoms). It is not clear what causes atopic people to behave differently. It might be that some environmental factors added to atopy (the genetic predisposition to allergy) stimulate the progression towards allergy or, as suggested by some new research data; it might be that expressing allergy requires an atopic predisposition and also other inherited genetic factors not related to production of IgE.