Cold temperatures cause decreased blood flow to the hands due to vasoconstriction, narrowing of the arteries caused by muscles in the blood vessel walls. This is a normal process that temporarily allows the body to send more blood to essential organs, such as the brain and heart, to keep them warm. In some cases, blood flow is reduced too much or for too long, leading to numbness.
Blood flows to the hand through two main arteries, the radial artery on the thumb side of the wrist and the ulnar artery on the pinkie side. Vasoconstriction caused by cold temperatures reduces blood flow through these arteries to move blood away from the hands to maintain warmth of the vital organs. This is a normal response to cold temperatures. As blood and oxygen delivery to the fingers decreases, numbness may develop. Reduced blood flow typically causes the fingers to appear pale or bluish, a characteristic called cyanosis.
As the hands warm up, blood rushes back in and causes them to become bright red. This restoration of blood flow can lead to pain or burning as sensation returns to the hand.
Primary Raynaud's phenomenon is an abnormal, exaggerated response to cool temperatures characterized by spasms in the arteries supplying blood to the hand. The cause of this condition is not known, although it typically develops in women during adolescence or early adulthood.
Exposure to cold temperatures or emotional distress triggers an attack, usually lasting several minutes. The fingers become numb and turn white as blood flow is markedly decreased. Cyanosis occurs shortly after as oxygen decreases in the fingers. Blood flow returns to the fingers when the attack is over.
Raynaud's phenomenon often gets worse with time. Attacks occur more frequently and blood flow is restricted for longer periods of time. Tissue in the fingertips may die with frequent, prolonged attacks. In severe cases, partial amputations may be necessary. Secondary Raynaud's phenomenon can be a side effect of another disease that affects the blood vessels, such as rheumatoid arthritis or lupus.
Raynaud's phenomenon is initially identified by color changes -- typically white to blue to red -- in the hand or fingers with exposure to cold. Doctors then need to determine whether it is an issue isolated to the hand -- primary Raynaud's phenomenon -- or part of another systemic condition -- secondary Raynaud's phenomenon.
Nailfold capillaroscopy is a test used to help primary and secondary Raynaud's phenomenon. Tiny blood vessels at the base of the fingernail are studied under a magnifier. If these blood vessels are normal, a diagnosis of primary Raynaud's phenomenon is made. Abnormal blood vessels usually indicate that the disorder is secondary to another condition.
Raynaud's phenomenon treatment is based on the severity of symptoms. Symptoms are prevented by avoiding exposure to cold temperatures, wearing gloves, wiggling the fingers and massaging the hands to keep them warm. For people with frequent or severe symptoms, medications may be prescribed to dilate the blood vessels. Options include calcium-channel blockers, alpha blockers and vasodilators.
Chemicals are sometimes injected into the hand to temporarily block nerves that cause blood vessel constriction. Surgical intervention is sometimes required to treat severe cases of this condition. Sympathectomy -- separation of nerves from blood vessels in the hand -- is performed to reduce the frequency of attacks. If blood flow is obstructed, procedures are performed to remove the blockage and reroute blood flow.
Numbness from prolonged exposure to cold temperatures can occur briefly in healthy hands. However, numbness is also a symptom of frostbite -- a dangerous condition that can cause permanent damage to the hands. Other symptoms of frostbite include "waxy" skin that is discolored -- yellow, pale, blue, white or gray -- and cold to the touch.
Seek medical attention immediately if you experience symptoms that may indicate frostbite. Early treatment improves your chance for a full recovery without permanent tissue damage.