I was looking up the effects of stress on skin on WebMD. It only talked about treatment and gave an very basic overview of one potential explanation, but not for the hives in particular. I just want to know, what’s the biological mechanism for stress hives?
The mechanism of stress hives (urticaria):
Stress, for example, emotional stress or insomnia triggers the mast cells in the skin to release histamine. Histamine dilates the small arteries in the skin and makes them "porous," which allows some fluid from the blood to escape into the space between the cells.
I spoke with a doctor the other day and they said that the body releases histamines when under stress. The histamines are there to attack foreign bodies, however there are none from stress. They then "attack" the skin and cause it to become inflamed and produce hives.