Lewis triple response is caused due to:

Lewis triple response is caused due to Histamine When histamine is injected intradermally it causes the triple response consisting of: Red spot: Due to capillary dilatation. Wheal: Due to exudation of fluid from capillaries and venules. Flare: Redness in the surrounding area due to aeriolar dilation mediated by axon reflex. A, 'Triple response' elicited by firm stroking of skin of forearm with a pencil. B, Diagrammatic view of microscopic features of triple response of the skin