Allergies - congenital situations or created and developed over the years?
Allergies are caused by one's immune system.  If you had never been exposed to the allergen, you would not experience any symptoms.  So they are not innate or inherent.

Why do people develop food allergies after repeated exposure?  I have not read any convincing explanations for the biology behind this.  When you look at the heavy-chain switching that takes place in B-cells, the IgE that are responsible for allergy symptoms are the terminal switch, so those antibody variable regions have already been selected during your life history up until that point.