點解食完鼻敏感藥會無事

抗過敏的藥，基本上是抗組胺。組胺是由你的身體釋放的炎症反應。當刺激物，如花粉進入你的身體，你的身體不承認那物質會釋放組胺保護你的身體(炎症反應的一部分)。抗過敏藥大多是抗組織胺是試圖抵消你身體的天然防禦。當藥物消失後，沒有更多的抗組胺對抗在你身體釋放的組胺。

這只是一個很簡單的解釋。如果您想了解更多，你可以研究組胺和炎症反應。

(用Google Translator, 原詞:)

anti-allergy medicine are basically anti-histamine. Histamine is release by your body in response to inflammatory reaction. When an irritant such as pollen enters your body, your body does recognize the substance and release histamine as part of the inflammatory response. Anti-allergy medicine are mostly anti-histamine that is trying to counteract the your body's natural defense. When the drug wears off, there is no more anti-histamine in your body to counteract the histamine release by your body.

This is just a very simply explanation. If you want to know more, you can research more about histamine and inflammatory response.