A shortage of oxygen in the blood causes a bluish tint to the skin or
mucous membrane. Cyanosis is the medical term for this condition.
Red blood cells transport oxygen throughout the body. Almost all red
blood cells in the arteries carry a full supply of oxygen most of the time.
The skin is pinkish or red, and the blood cells are bright red. Blood that
has been depleted of oxygen is a dark bluish-red colour. People with
low oxygen levels in their blood have a bluish tint to their complexion.