Cyanosis is a condition of bluish, grayish, slatelike or dark purple discolouration of the skin, seen particularly about the face and extremities (nails, tips of ears). It accompanies states in which the blood is not properly oxygenated in the lungs or there is reduced haemoglobin in the blood.
It may be due to blockage of the air passages, or to disease in the lungs, or to a feeble circulation, as in heart disease.