Dermatographism

When this patient’s skin is briskly stroked with a firm object (such as the edge of a tongue depressor or the edge of a fingernail), a linear wheal with a flare immediately develops and typically lasts about 30 minutes. Dermatographism (also known as dermographism) is considered a form of physical urticaria. In fact, its presence is often used to bolster the diagnosis of urticaria, since the prevalence of dermatographism in patients with chronic idiopathic urticaria is about 22%.

It is thought to be caused by the extravasation of plasma, which results from histamine released by the physical degranulation of mast cells. Urtication can also be seen in forms of mastocytosis.