system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do mosquito bites itch?
gpt
There is a substance in there saliva that works as an anti-clotting agent. Almost all humans are allergic to this substance. A bite won't itch strait away because the saliva also contains a local anesthetic that dulls the pain and irritation of the bite so the mosquito can stay undetected. But when this anaesthetic stops working the bite becomes itchy.