The term dermographism (or dermatographism) literally means writing on the skin. Firm stroking of the skin produces an initial red line (capillary dilatation), followed by an axon-reflex flare with broadening erythema (arteriolar dilatation) and the formation of a linear wheal (transudation of fluid/edema); these events are collectively termed the triple response of Lewis.
An exaggerated response to this constitutional whealing tendency is seen in approximately 2-5% of the population and is referred to as dermographism. In a minority of people, it is accompanied by itching (symptomatic dermographism).
See the image below.
Dermographism should be distinguished from other types of urticaria. See the following articles:
Pathophysiology and Etiology
The exact mechanism of dermographism remains uncertain. Trauma may release an antigen that interacts with the membrane-bound immunoglobulin E (IgE) of mast cells, which release inflammatory mediators, particularly histamine, into the tissues. This process causes small blood vessels to leak, allowing fluid to accumulate in the skin. Other mediators that may be involved are leukotrienes, heparin, bradykinin, kallikrein, and peptides such as substance P.
Symptomatic dermographism is usually idiopathic, though it may have an immunologic basis in some patients. Passive transfer of the dermographic response with IgE- or immunoglobulin M (IgM)-containing serum has been reported, but no allergen has been identified.
Symptomatic dermographism may be triggered by drugs (eg, penicillin), an insect bite, Helicobacter pylori infection, or an infestation (eg, scabies, Fasciola hepatica). Congenital symptomatic dermographism has been described as the first sign of systemic mastocytosis. 
Approximately 75% of patients with hypereosinophilic syndrome, which has multisystem involvement and high mortality, have dermographism. Psychological factors and a history of stressful life events have been implicated as triggering factors in 30% of patients.  However, a small prospective study showed no alteration in dermographic reaction after social stress provocation tests. 
Dermographism is the most common of the physical urticarias and can occur with other forms of urticaria. An increased incidence has been reported during pregnancy (especially in the second half), at the onset of menopause, in atopic children, and in patients with Behçet disease. 
Dermographism can appear in persons of any age but is more common in young adults; the peak incidence is in the second and third decades. Whether a sexual variance in prevalence occurs is unclear. None has been consistently reported, though one study on dermographism in children reported a female predominance.  No racial variance in prevalence is known.
Simple dermographism is the most common variant, and patients with this form are asymptomatic. However, other forms are associated with pruritus, and this can significantly affect quality of life. Most people with dermographism are otherwise healthy. An association with thyroid disease has been described in some patients but remains controversial.
The natural history of symptomatic dermographism is unpredictable. It may last for months or years, or be present intermittently. In many patients, the condition gradually improves and clears after several years. Of the chronic urticarias, symptomatic dermographism appears to have the best prognosis in terms of clearance after 5 years (36%) and 10 years (51%). 
Reassure patients about the benign nature of the disorder, and inform them of the possible prolonged course. Explain the adverse effects of antihistamine therapy. In particular, warn patients about drowsiness, which is especially problematic when they are driving or handling machinery.