What is the difference between dermographism and hives?

Both signs of allerg: Dermatographism is the welting up of skin when it is stroked with a dull object such as a fingernail. The welt will be exactly the same pattern as what is "drawn" on the skin. Hives are spontaneous welts, usually circular that occur when someone is exposed (usually by eating) something they are allergic to. They are both seen in allergic people.

Similar: Dermographism is a form of physical urticaria (hives) caused by a physical stimulus (scratching). "hives" in general can be caused by other triggers in addition to physical stimuli--other triggers for hives include infection, drug allergy, food allergy, autoimmunity, idiopathic, etc.