The skin discoloration occurs because an abnormal spasm of the blood vessels causes a diminished blood supply. Initially, the digits involved turn white because of diminished blood supply, then turn blue because of prolonged lack of oxygen and finally, the blood vessels reopen, causing a local "flushing" phenomenon, which turns the digits red. This three-phase color sequence (white to blue to red), most often upon exposure to cold temperature, is characteristic of Raynaud's phenomenon.
Raynaud's phenomenon occurs with a number of conditions including rheumatic diseases (scleroderma, rheumatoid arthritis, systemic lupus erythematosus), hormone imbalance (hypothyroidism and carcinoid), trauma (frostbite, vibrating tools), medications (propranolol/INDERAL, estrogens, nicotine, bleomycin) and, uncommonly, cancer.
The phenomenon is named for the French physician Maurice Raynaud (1834-1881).