Cyanosis refers to the bluish coloration of the skin due to the presence of deoxygenated blood in blood vessels near the skin surface.

Cyanosis can occur in the fingers and extremities (called peripheral cyanosis), or in the lips and face (central cyanosis).

Peripheral cyanosis suggests that there is poor circulation in the small vessels involved, such as when a person's hands are very cold.

Central cyanosis suggests a circulatory or ventilatory problem that leads to poorer blood oxygenation in the lungs or greater oxygen extraction due to slowing down of blood circulation in the skin's blood vessels. The extent of central cyanosis depends also on the blood hemoglobin concentration. The greater the concentration the more easily cyanosis develops.