Cyanosis is a bluish color to the skin or mucus membranes due to a lack of oxygen in the blood.

The coloration of the skin is caused by the amount of pigment in the skin and the blood flowing through it. Blood that is saturated with oxygen is bright red. 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.

Cyanosis can be caused by:

• Lack of oxygen (such as in suffocation or cyanotic heart disease)
• Abnormal hemoglobin (such as methemoglobinemia)
• Toxins (such as cyanide)

Most cyanosis occurs as a result of:

• Heart disease (such as congestive heart failure)
• Lung disease
• A potentially fatal event, such as the stopping of heart and lung function (cardiopulmonary arrest)

Mild cyanosis may be hard to detect. Usually the oxygen saturation of the blood has to drop from the normal level of nearly 100% to below 90% before cyanosis occurs.

In dark-skinned people, cyanosis may be easier to see in the mucus membranes (lips, gums, around the eyes) and nail beds, rather than in the skin. It may also appear on the feet, nose, and ears.

People with a problem called Raynaud's phenomenon may develop a blue color in their fingers or hands when they are exposed to cold.

A blood clot that blocks the blood supply to a leg, foot, hand, or arm will cause bluish skin.

Other causes of bluish skin (cyanosis) include:

Problems with the lungs

• Pneumonia (severe)
• Bronchiolitis
• Chronic obstructive pulmonary disease (COPD), asthma, and other chronic lung problems
• Blood clot in the arteries of the lungs (pulmonary embolism)
• Hyaline membrane disease due to prematurity
• Pulmonary hypertension

Problems with the airways leading to the lungs

• Choking on something stuck in the airways
• Croup
• Epiglottitis

Problems with the heart

• The heart stops working (cardiac arrest)
• Heart failure
• Heart defects that are present at birth (congenital)

Other problems

• Exposure to cold air or water
• High altitudes
• Breath-holding
• Seizures that last a long time
• Drug overdoses (narcotics, benzodiazepines, sedatives)
• Toxins such as cyanide
• Drowning or near-drowning