What can cause my hands to turn completely blue for no reason. it was warm not hot or cold. ?

Follow up: Bluish hands mean blood has lost its oxygen is dark bluish-red. People whose blood is low in oxygen tend to have a bluish color to their skin, called cyanosis. Depending on the cause, cyanosis may develop suddenly, along with shortness of breath and other symptoms. Cyanosis that is caused by long-term heart or lung problems may develop slowly need to see a cardiology and pulm doctor