Cyanosis is a 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.


Red blood cells contain a red pigment called hemoglobin. 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.

Cyanosis in infants

When cyanosis occurs in infants, it is often called blue-baby syndrome. Blue-baby syndrome may occur in infants who drink water with a high concentration of nitrate or are fed formula prepared with water containing high nitrate levels. Excess nitrate can result in methemoglobinemia, a condition in which the oxygen-carrying capacity of the blood is impaired by an oxidizing agent such as nitrite, which can be reduced from nitrate by bacterial metabolism in the human mouth and stomach. Infants in the first three to six months of life, especially those with diarrhea, are particularly susceptible to nitrite-induced methemoglobinemia.

A molecule that carries oxygen to tissues and gives blood its red color.
A condition in which the oxygen-carrying capacity of the blood is impaired by an oxidizing agent.
Respiratory distress syndrome—
Also known as hyaline membrane disease, 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.

Adults convert about 10% of ingested nitrates into nitrites, and excess nitrate is excreted by the kidneys. In infants, however, nitrate is transformed to nitrite with almost 100% efficiency. The nitrite and remaining nitrate are absorbed into the body through the intestine. Nitrite in the blood reacts with hemoglobin to form methemoglobin, which does not transport oxygen to the tissues and body organs. The skin of the infant appears blue due to the lack of oxygen in the blood supply, which may lead to asphyxia, or suffocation. Normal methemoglobin levels in humans range from 1 to 2%; levels greater than 3% are defined as methemoglobinemia. Methemoglobinemia is rarely fatal, readily diagnosed, and rapidly reversible with clinical treatment.


Domestic water supply wells may become contaminated with nitrate from mineralization of soil organic nitrogen, septic tank systems, and some agricultural practices, including the use of fertilizers and the disposal of animal wastes. Since there are many potential sources of nitrates in groundwater, the prevention of nitrate contamination is complex and often difficult.

Other signs of low blood oxygen may accompany cyanosis, including feeling lightheaded or fainting.


Cyanosis is rare among otherwise healthy individuals, including infants in developed parts of the world. One study found only 2,000 cases of blue-baby syndrome in North America and Europe between 1945 and 1971, with only one death reported in the last decade of that period. The World Health Organization stated that blue-baby syndrome in the world is rare, although there are no statistics on the condition.


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


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


Cyanosis in infants can be prevented by removing nitrates and nitrites from drinking water by using any one of several types of technologies. The Environmental Protection Agency (EPA) has designated reverse osmosis, anion exchange, and electrodialysis as the best available control technologies (BATs) for the removal of nitrate, while recommending reverse osmosis and anion exchange as the BAT for nitrite. Other technologies can be used to meet MCLs for nitrate and nitrite if they receive approval from the appropriate state regulatory agency.

See also Carbon monoxide poisoning ; Environmental Protection Agency (EPA) ; Methemoglobinemia ; World Health Organization .



Snider, H. L. “Cyanosis.” In Clinical Methods: The History, Physical, and Laboratory Examinations, 3rd ed., edited by H. Kenneth Walker, W. Dallas Hall, and J. Willis Hurst. Cambridge, MA: Butterworths, 1990.


Ellis, Collin L., John C. Rutledge, and Mark A. Underwood. “Probiotic Therapy for Term Neonates with Cyanotic Congenital Heart Disease.” Gut Microbes 1, no. 6 (2010): 359–66.

Faust, B. “Nitrate and the Blue Baby Syndrome.” Education in Chemistry 41 (2004): 44–46.

Powlson, D. S., T. M. Addiscott, N. Benjamin, et al. “When Does Nitrate Become a Risk for Humans?” Journal of Environmental Quality 37, no. 2 (2008): 291–95.


Howard Hughes Medical Institute. “Homing in on the Cause of Blue Baby Syndrome.” (accessed September 20, 2012).

Medline Plus. “Methemoglobinemia.” (accessed September 20, 2012).


American Academy of Pediatrics (AAP), 141 Northwest Point Blvd., Elk Grove, IL, 60007-1098, (847) 434-8000, .

National Institute of Child Health and Human Development (NICHD), PO Box 3006, Rockville, MD, 20847, (800) 370-2943, Fax: (866) 760-5947, NICHDInformation, .

Carol A. Turkington
David Newton, EdD

  This information is not a tool for self-diagnosis or a substitute for professional care.