What is Darier’s sign?

It is found in patients who suffer with mastocytosis and have skin involvement (multiple brown-red macules, usually on the trunk). They “urticate” (get red, itchy, swollen) when they are touched.

Systemic mastocytosis is a cause of severe or fatal anaphylaxis. Management is with adrenaline, but they often require larger doses.

You can read a nice review article here.