Red blood cells provide oxygen to body tissues. Most of the time, almost all red blood cells in the arteries carry a full supply of oxygen. These blood cells are bright red and the skin has a pinkish or red hue.
Blood that 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. Symptoms may be present, but are often not severe.
When oxygen levels have dropped only a small amount, cyanosis may be hard to detect.
In dark-skinned people, cyanosis may be easier to see in the mucus membranes (lips, gums, around the eyes) and nails.