Darier's sign is a change observed after stroking the skin of a person with systemic mastocytosis or urticaria pigmentosa.
In general, the skin becomes swollen, itchy and red. This is a result of compression of mast cells, which are hyperactive in these diseases. These mast cells release inflammatory granules which contain histamine. It is the histamine which is responsible for the response seen after rubbing the skin.
Read more about Darier's Sign: Eponym
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