Raynaud's phenomenon occurs when the blood vessels in the fingers and toes react to cold temperatures or stress by contracting and reducing blood flow. The reduced blood flow caused by Raynaud's phenomenon often results in digits turning blue or white due to a lack of blood. It is usually a minor condition and fingers and toes generally return to normal within 15 minutes as arteries relax and the body warms up. 

Around one in ten people in the United States have some form of Raynaud's, the most common form of which is primary Raynaud's phenomenon. Primary Raynaud's phenomenon occurs when there is no underlying ailment causing the condition. Secondary Raynaud's phenomenon is when the condition is caused by another disease, such as lupus or rheumatoid arthritis.

Treatment of Raynaud's phenomenon usually focuses on keeping warm, avoiding stress, and taking medication to relax blood vessels. Drug classes commonly used to treat the condition are dihydropyridine calcium channel blockers and anti-arrhythmics, class IV.