Raynaud's syndrome, first described in 1862, is a relatively common medical condition in which extreme vaso-constriction of the peripheral blood vessels leads to reduced blood flow in the minor arteries of the fingers and toes, and in some cases the nose, ears, or lips.

The symptoms typically last from a few minutes to a few hours.

Doctors classify the syndrome into two types. The first, 'Primary Raynaud's' is the most common - thought to affect around 10 million people in the UK alone. (ref )

Aside from its association with exposure to cold, its cause is unclear :

It is likely that primary Raynaud's is caused by certain disruptions to the way that the nervous system controls blood vessels, although exactly what causes these disruptions remains unknown.

Source : SRUK

The second, less common variant, is known to be a result of other diseases such as Lupusplugin-autotooltip__plain plugin-autotooltip_bigLupus

"Systemic lupus erythematosus, also called SLE or lupus, is a disease of the immune system that causes the immune system to attack tissues in various parts of the body. The cause of lupus is unknown. Finding the cause is the object of major research efforts..

Episodes of 'Primary Raynaud's' are typically brought on by cold or emotional stress. It has even been called "an allergy to coldness". Smoking and caffeine can exacerbate the attacks.

Also see : Perniosisplugin-autotooltip__plain plugin-autotooltip_bigPerniosis

Perniosis (a.k.a. Chilblains) is a seasonal condition triggered by prolonged exposure to cold and humidity. It typically affects the toes, where inflammation of the small blood vessels lead to painful, itchy, tender, skin injuries. The lower legs, hands, ears and face can also be affected.