The triad of Lewis ( The triples response Lewis off. English ), proposed by Sir Thomas Lewis (1881-1945) in 1927 to explain the physiopathogénie Papule S found in the Urticaria, is the appearance, after friction of the skin of a lesion completely identical to that of the Urticaire, reproducing:

1. a vasodilatation responsible for the erythema (redness) clinical.

2. a stressing of the vascular permeability leading to the edema (swelling).
3. a reflex of axon leading to neighbouring dilation artériolaire thus with the extension of the erythema.

See too

• Urticaria and angioœdème

• Changes in Vessel Gauges
• Lewis T. The Blood Vessels off the Skin and to their Responses . London, Shaw and Sounds, ED., 1927.