histamine
This substance has a general name called an antigen.
Some more context would be helpful. This question sounds like it may be asking about antigen exposure in the field of allergic disease, but it's hard to be sure. Hypersensitivity reactions (the immune system basis for allergies) are based on the principle that allergy follows initial sensitization to an antigen.
Antigen
It is called Cross Contact. It can also be called Cross Contamination.
The 'Initial'
NO
NO
An allergy is the reaction that the body will have, where as an allergen is something that causes the allergy to occur.
deciduous
Gatsby first met Daisy in Louisville, Kentucky, when he was a young officer stationed near her home. Their initial encounter had a significant impact on their relationship as they fell in love, but were separated due to social class differences and external circumstances. This encounter set the foundation for their complicated and ultimately tragic relationship in F. Scott Fitzgerald's novel "The Great Gatsby."
antibodies are formed when the immune system comes in contact with the allergen.