Triple response of Lewis

The triple response consists of three aspects: The red spot emerges within 15 seconds.

[citation needed] The triple response of Lewis is particularly sensitive in people with dermatographia urticaria.

Histamine, or 2-(imidazol-4-yl)ethanamine, is a dibasic vasoactive amine that is located in most body tissues but is highly concentrated in the lungs, skin, and gastrointestinal tract.

Found in tissues throughout the body, they are particularly associated with blood vessels and nerves, and are in proximity to surfaces that border the external environment.

The underlying pathophysiology of frostbite is a combination of freezing, vascular insufficiency (constriction and occlusion) and damage due to inflammatory mediators.