The Siberian air mass that sent temperatures plunging recently has resurrected a winter health threat: frostbite.

Skin exposed for long periods to very cold temperatures freezes and is damaged according to the degree of exposure, with the worst cases involving underlying tissue.Frostbitten skin is pale or bluish, hard and insensitive to touch. After thawing, it turns red and is extremely painful. It usually blisters. Extremities such as fingers and toes are the most susceptible to frostbite and should be well-insulated in the cold.

Parts of the body that are badly frostbitten may never completely recover and sometimes must be amputated, though most cases are far less severe.

Mild frostbite requires a slow and gentle warming of the tissue as soon as possible.