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Definition of Carbon Dioxide


Updated February 18, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.


Carbon dioxide is a colorless, odorless gas. Its chemical compound consists of one atom of carbon covalently bonded to two atoms of oxygen. Carbon dioxide is represented by the chemical formula CO2. It may form by the burning of carbon or organic materials and is sometimes referred to as the greenhouse gas, with a role in global warming. It naturally makes up about 0.03% of air. It is absorbed by plants during photosynthesis.

Carbon dioxide is also created by metabolism within the human body and it is principally removed via expiration from the lungs. It therefore can build up in the blood when breathing becomes disrupted. High levels of carbon dioxide may cause drowsiness and -- at the most extreme levels -- unconsciousness, coma, and death.

The retention of carbon dioxide in the blood is an important consequence of a handful of sleep disorders that affect breathing, especially sleep apnea, central hypoventilation syndrome, and obesity hypoventilation syndrome.

Also Known As: CO2
Carbon dioxide becomes too high in the blood when breathing is disrupted.
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