Raynaud's phenomenon is one of the most common microvascular conditions. It causes small vessels of the skin's extremities to constrict in response to cold or emotional stimuli. Skin colour may change and affected areas (usually fingers and toes) feel cold and numb.
Raynaud's phenomenon occuring in isolation is termed 'primary'. More rarely 'secondary' Raynaud's may occur, arising from other causes such as autoimmune connective tissue diseases.