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Cyanosis is a physical sign causing bluish discoloration of the skin and mucous membranes. Cyanosis is caused by a lack of oxygen in the blood. Cyanosis is associated with cold temperatures, heart failure, lung diseases, and smothering. It is seen in infants at birth as a result of heart defects, respiratory distress syndrome, or lung and breathing problems.


Blood contains a red pigment (hemoglobin) in its red blood cells. Hemoglobin picks up oxygen from the lungs, then circulates it through arteries and releases it to cells through tiny capillaries. After giving up its oxygen, blood circulates back to the lungs through capillaries and veins. Hemoglobin, as well as blood, is bright red when it contains oxygen, but appears dark or "bluish" after it gives up oxygen.
The blue discoloration of cyanosis is seen most readily in the beds of the fingernails and toenails, and on the lips and tongue. It often appears transiently as a result of slowed blood flow through the skin due to the cold. As such, it is not a serious symptom. However, in other cases cyanosis is a serious symptom of underlying disease.

Causes and symptoms

The blue color of the skin and mucous membranes is caused by a lack of oxygen in the blood. Low blood oxygen may be caused by poor blood circulation, or heart or breathing problems. It can also be caused by being in a low-oxygen environment or by carbon monoxide poisoning. More rarely, cyanosis can be present at birth as a sign of congenital heart disease, in which some of the blood is not pumped to the lungs where oxygen would make the blood a bright red color. Instead, the blood goes to the rest of the body and remains unoxygenated. Cyanosis also may be caused by poisoning from chemicals, drugs, or contaminated food and water.
Other signs of low blood oxygen may accompany cyanosis, including feeling lightheaded or fainting.


Treatment of the underlying disease can restore proper color to the skin.

Key terms

Hemoglobin — A colored substance (pigment) in the blood that carries oxygen to tissues and gives blood its red color.
Respiratory distress syndrome — Also known as hyaline membrane disease, this is a condition of premature infants in which the lungs are imperfectly expanded due to a lack of a substance on the lungs that reduces tension.


If the underlying condition (such as heart or lung disease) can be properly treated, the skin will return to its normal shade.



Carolson, Karen J., Stephanie A. Eisenstat, and Terra Ziporyn. The Harvard Guide to Women's Health. Cambridge, MA: Harvard University Press, 1996.


a bluish discoloration of the skin and mucous membranes due to excessive concentration of reduced hemoglobin in the blood. adj., adj cyanot´ic.
central cyanosis that due to arterial unsaturation, the aortic blood carrying reduced hemoglobin.
enterogenous cyanosis a syndrome due to absorption of nitrites and sulfides from the intestine, principally marked by methemoglobinemia and/or sulfhemoglobinemia associated with cyanosis, and accompanied by severe enteritis, abdominal pain, constipation or diarrhea, headache, dyspnea, dizziness, syncope, anemia, and, occasionally, digital clubbing and indicanuria.
peripheral cyanosis that due to an excessive amount of reduced hemoglobin in the venous blood as a result of extensive oxygen extraction at the capillary level.


A dark bluish or purplish discoloration of the skin and mucous membrane due to deficient oxygenation of the blood, evident when reduced hemoglobin in the blood exceeds 5 g/100 mL.
[G. dark blue color, fr. kyanos, blue substance]


A bluish discoloration of the skin and mucous membranes resulting from inadequate oxygenation of the blood.

cy′a·not′ic (-nŏt′ĭk) adj.
An abbreviation—Cyanosis, Clubbing, Edema—used in physical examination of the extremities, which is a crude indicator of adequate oxygenation of blood


Physical examination A bluish discoloration of skin and mucosae due to excessive concentration of reduced Hb in the blood. See Hypoxia.


A dark blue or purple discoloration of the skin, nail beds, lips, or mucous membranes seen with sulfmethemoglobin concentrations of 0.5 g per 100 mL or greater, methemoglobin concentrations of 1.5 g per 100 mL or greater, or deoxyhemoglobin concentrations of 5.0 g per 100 mL or greater.


Blueness of the skin from insufficient oxygen in the blood. Fully oxygenated blood is bright red and imparts a healthy pinkness to the skin. Blood low in oxygen is dark reddish-blue and, through the skin, looks a dusky blue. Cyanosis may be due to lung disease, HEART FAILURE or disorders, especially congenital heart disease, in which, blood is shunted away from the lungs. ‘Blue babies’ have cyanosis.


bluish discolouration of the skin and lining of the mouth due to lack of OXYGEN in the BLOOD.


A dark bluish or purplish discoloration of the skin and mucous membrane due to deficient oxygenation of the blood.