system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do allergies develop in kids?
gpt
Basically, the body encounters something it hasn't encountered before. It usually is a foreign protein. The body encounters it and thinks that it is something bad that is trying to harm the person. The body then creates an immune response to protect the body. The next time the body encounters this allergen it reacts as if it is trying to harm the body, leading to an allergic response. This often means massive release of histamine which can cause swelling of the lips, tongue, throat, and gut in the case of a serious anaphylactic reaction.

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Source: Am doctor.