(1) the triphasic response to the firm stroking of the skin. Phase 1 is the sharply demarcated erythema that follows a momentary blanching of the skin and is the result of release of histamine from the mast cells. Phase 2 is the intense red flare extending beyond the margins of the line of pressure but in the same configuration, and is the result of arteriolar dilation; also called axon flare because it is mediated by axon reflex. Phase 3 is the appearance of a line wheal in the configuration of the original stroking. (2) A similar response resulting from an intradermal injection of histamine.