What Is Carbon Monoxide?

CO is a poisonous gas that binds strongly to hemoglobin

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Carbon monoxide is an odorless, tasteless, poisonous gas that forms when carbons from fuels burn incompletely. It is lighter than air and released both naturally, such as from forest fires and volcanic eruptions, and through man-made processes.

Some common man-made releases of carbon monoxide are from fumes of vehicles, small engines (like those in lawnmowers and generators), stoves, fireplaces and furnaces.

Carbon monoxide, or CO, is composed of one molecule of carbon and one molecule of oxygen, held together by a triple bond.

Carbon Monoxide Poisoning Symptoms

Theresa Chiechi / Verywell

How It Works

Carbon monoxide has a powerful ability to affect cell metabolism, as it can cause reactions that deprive cells of oxygen. 

This comes from the capacity of carbon monoxide to bind strongly to heme, an iron compound in hemoglobin, which carries oxygen to the tissues of the body. This bonding can change the function of the heme proteins. Carbon monoxide’s affinity to bind with hemoglobin is more than 200 times greater than that of oxygen for hemoglobin.

When carbon monoxide bonds with heme, it forms carboxyhemoglobin (COHb) and decreases the oxygen-carrying capacity of the blood. It also disrupts the release of oxygen already attached to the hemoglobin, so it can’t be released into tissues.

Another way carbon monoxide disrupts the body’s systems is by diminishing the oxygen storage in muscle cells by binding to and displacing oxygen from myoglobin.

All areas of the body suffer from this toxicity, but the most vulnerable tissues to this suffocation are the organs that use the most oxygen, like the brain and heart. The developing nervous system is particularly sensitive to carbon monoxide. People with ongoing cardiovascular or respiratory disease may also be compromised and unable to fight off the effects of carbon monoxide.

Carbon monoxide can also create effects that are unrelated to the supply of oxygen. In meat processing, carbon monoxide reacts with myoglobin and forms carboxymyoglobin, passing on a red appearance to the meat.


Carbon monoxide has a variety of uses in manufacturing and medical products.


Carbon monoxide is used in the production of hydrogen, heterogeneous catalysts, pure metals, acetic anhydride, formic acid, methyl formate, N,N-dimethylformamide, propanoic acid, and as a reducing agent in blast furnaces.

It is used to create other chemicals, including methanol, which is used to make fuel and solvents, and phosgene, an industrial chemical used to make pesticides and plastics. It is also used in some lasers that cut glass.

Carbon monoxide is used in the production of acrylic acid, a compound used in diapers, water treatment, and textiles.


Carbon monoxide can be used to create aluminum chloride, a chemical in skin medications.

The gas is used as a marker of respiratory status in spirometry, or lung function tests. Carbon monoxide is inhaled in small amounts because it mimics the behavior of oxygen in the body. The output of carbon monoxide can show doctors how well a person’s lungs are transferring gases, such as oxygen, into the bloodstream.

Carbon monoxide is being tested in several clinical trials as therapy for respiratory conditions such as acute respiratory distress syndrome (ARDS), which often affects military personnel and veterans, and has a high mortality rate. Researchers have found that inhalation of low doses of carbon monoxide can protect against further lung injury.

Food Processing

Carbon monoxide is often used in small amounts as a food additive to keep meat looking red. Carbon monoxide additives are approved by the Federal Department of Agriculture in the packaging of red meat. 

Meat producers have reported it stabilizes the red color for up to 20 days, which helps prevent food waste; consumers are wary of any meat that turns brown, thinking it has spoiled.


A variety of fumigants, including carbon monoxide, are used to kill rodents in agriculture. Carbon monoxide kills rodents by reducing the amount of oxygen transmitted to their cells. 

Risks and Hazards

Carbon monoxide is known as a “silent killer” as it is poisonous, acutely toxic, and potentially lethal in certain doses. It is also extremely flammable and classified as a health hazard.

Carbon monoxide poisoning can cause illness, hospitalization, and death. Because it has no odor or color, it often goes undetected, striking unsuspecting victims in sleep or states of drunkenness.

Each year, more than 400 people in the United States die from accidental carbon monoxide poisoning, more than 20,000 are seen in the emergency room, and more than 4,000 are hospitalized. Poisoning is measured in a range called parts per million, and when levels of carbon monoxide reach 150 ppm, people can become disoriented and collapse.

Carbon monoxide build-up is not necessarily a result of a malfunctioning appliance. When the gas concentrates in a small area and cannot dissipate, people and animals can get poisoned. Being in an open garage with a running car also can cause carbon monoxide poisoning, and so can using a portable grill or generator indoors for heat.


Symptoms of carbon monoxide poisoning can be fairly general and hard to pinpoint:

  • Headache
  • Dizziness
  • Weakness
  • Upset stomach
  • Chest pain
  • Vomiting
  • Confusion

CO Poisoning Can Be Deadly

Sometimes the poisoning effects are described as similar to flu symptoms. Too much inhaled carbon monoxide can cause loss of consciousness and death.

Prevention of Carbon Monoxide Poisoning

As it is the second-leading cause of poisoning in the United States, it's helpful to know carbon monoxide poisoning prevention methods. Some actions you can take are:

  • Install a battery-operated carbon monoxide detector in your home.
  • Have your home’s heating system, water heater, and other gas, oil, or coal-burning appliances serviced each year.
  • Never use portable, flameless chemical heaters indoors.
  • If you smell an odor from your gas-powered refrigerator, call a repair service.
  • Have your chimney checked and cleaned each year.
  • Have a mechanic check your car or truck’s exhaust system for leaks each year.
  • Never use a gas range or oven for heating indoor spaces.


Carbon monoxide is legal within the use limits prescribed by government health and safety bodies.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health ClinicalTrials.gov. Safety and efficacy study of inhaled carbon monoxide to treat acute respiratory distress syndrome (ARDS).

  2. Djenane D, Roncalés P. Carbon monoxide in meat and fish packaging: Advantages and limitsFoods. 2018;7(2):12. doi:10.3390/foods7020012

  3. Centers for Disease Control and Prevention. Carbon monoxide poisoning: Frequently asked questions.

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