Today I accidentally ingested something that I’m mildly allergic to, and within minutes I had hives on my shoulders and scalp (which is my usual reaction).
I understand that hives are caused by your immune system being activated. What I don’t understand is: if you’ve just ingested the food you’re allergic to, how is it that your immune system gets activated before you’ve had any time to digest it? And why do hives appear on the scalp, which is far away from where the food would be absorbed?
In: Biology
Hives are caused by whatever you ate binding to an antibody that hangs out in your blood that activates a special kind of immune cell, called a “mast cell.” When the mast cell is activated, it triggers a bunch of other immune cells to activate and releases chemicals like histamine that make your blood vessels leaky, allowing immune cells and fluid to get from vessels into the peripheral tissues, like the skin of your scalp, causing hives and swelling. This all happens super fast.
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