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First encounter
The allergen is consumed, but there is not a negative physical reaction yet. In this stage, the body recognizes the allergy and the antibody is formed, thus will react the next time it is consumed. -
Second encounter
When the allergen is consumed for the second time, the system immediately recognizes the problem and binds to the antibodies, sending out copious amounts of histamine which is what causes the swelling in the throat, lips, etc..