Cyanosis, sy uh NOH sihs, is a medical condition involving a bluish tint of the skin and mucous membranes. Cyanosis results if the blood flowing through vessels in the skin and mucous membranes contains too much reduced hemoglobin--that is, hemoglobin not combined with oxygen. Hemoglobin is the compound in red blood cells that carries oxygen. When combined with oxygen, hemoglobin makes blood bright red. Blood containing large amounts of reduced hemoglobin appears bluish when seen through the skin and mucous membranes.