Blue discoloration of the fingers or nails, known as cyanosis, usually occurs when normal oxygen flow in the body is interrupted, Healthline states. Whether temporary or recurrent, Raynaud's syndrome may cause the condition, or a defect of the lungs of heart may trigger it.
Cyanosis can occur rapidly when a person is choking or having a seizure, according to Healthline. When the condition is related to chronic heart or lung diseases, it usually develops slowly over time from conditions such as asthma, chronic obstructive pulmonary disease or congestive heart failure
Cyanosis develops when red blood cells are unable to deliver an adequate oxygen supply to body tissue, causing the blood to turn dark bluish-red, according to MedlinePlus. The condition can produce discoloration throughout the body, but it is often difficult to detect, especially in darker skin. When cyanosis only affects one hand, it is most likely caused by Raynaud's syndrome or a blot clot that is temporarily limiting oxygen flow in the hand.
During periods of stress or exposure to cold, Raynaud's syndrome triggers repeated episodes of constricted blood vessels in the fingers and toes, causing numbness, Cleveland Clinic states. The most common form, primary Reynaud's syndrome, occurs spontaneously with no underlying cause, while the secondary form is related to pre-existing medical conditions, such as heart disease or carpal tunnel syndrome. People living in cold environments are more likely to be affected because narrowed blood vessels interfere with the body's attempts to conserve heat.