system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the itch of a mosquito bite 'go away' and then 'come back' hours later?
gpt
I dont know for sure but it sounds like a direct and a late allergic respons. Typed really quickly:

First there is a direct activation of mastcells by IgE specific for molecules in the musquito's saliva, these mast cells degranulate and the histamine causes swelling, the proteases and attracked neutrophils causes local damage thus irritation.

After a few hours, around 4, the late onset repons of t-lymphocytes begins. This second and slower allergic immune respons creates again some more swelling and local irritation. 

Patients with an allegic shock for example in a bee sting, can experience a second a few hours later. So even when they are stable again, they are taken to the hospital for observation.