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.

It typically appears 12-24 hours after exposure to cold and usually lasts for two to three weeks.

Although some instances of perniosis can be attributed to the effects of other diseases (e.g. Raynaud's syndromeplugin-autotooltip__plain plugin-autotooltip_bigRaynaud's syndrome

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., erythromelalgia and 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. etc) the common type, which is related to cold exposure, has biophysical mechanisms that have not yet been fully explained.

One hypothesis is that the cold causes small blood vessels to contract, and that this can lead to oxygen deficiency and cell damage - but the exact mechanism is currently unknown.

Further information UK NHS