What Is Carbon Monoxide Poisoning?

Carbon monoxide (CO) is an odorless, colorless gas produced whenever something burns. Carbon monoxide poisoning occurs when someone breathes in this gas and can cause effects ranging from headache and nausea to coma and death. More than 400 Americans die from unintended carbon monoxide poisoning each year, making it the leading cause of death by poisoning in the United States.

Older adults, infants, and people living with certain chronic illnesses like asthma, anemia, or heart disease may be at greater risk of becoming ill from carbon monoxide poisoning. Engaging in physical activity during exposure may also lead to an increased risk of sickness.

Despite its danger, there are many ways to prevent this poisoning and you can be alerted to the gas’ presence with a carbon monoxide detector.

Symptoms of Carbon Monoxide Poisoning

The symptoms of carbon monoxide poisoning are broad and highly variable. They are also nonspecific, meaning they are symptoms for a wide range of conditions. This makes carbon monoxide poisoning easy to misdiagnose.

One common misdiagnosis, particularly for less severe carbon monoxide poisoning, is an acute viral illness such as the flu. The majority of CO exposures are reported between November and March, a time period known for viral infections. America’s Poison Centers. Seasonal poisoning hazards. Some common symptoms of mild to moderate poisoning include:

  • Headache
  • Dizziness
  • Weakness and fatigue
  • Nausea and vomiting
  • Increased heart rate
  • Chest pain
  • Shortness of breath
  • Difficulty concentrating
  • Confusion
  • Changes in vision.

Severe carbon monoxide poisoning can lead to long-lasting effects and death. Signs of severe poisoning include:

  • Seizures
  • Fainting or temporary loss of consciousness
  • Coma
  • The toxic build-up of lactic acid in your body
  • Damage to your heart muscle
  • Dangerous heart rhythms like ventricular tachycardia or ventricular fibrillation

Symptoms of Delayed Neurologic Syndrome

Delayed neurologic syndrome (DNS) is a condition caused by carbon monoxide poisoning that can cause changes in personality as well as movement and cognitive ability. It is called “delayed” because these changes occur after other signs of poisoning have resolved. These symptoms usually appear within three weeks of exposure but have been recorded to begin up to 240 days later.

Symptoms of CO Poisoning vs the Flu

People who confuse carbon monoxide poisoning symptoms for the flu may ignore mild symptoms until they become too sick to rescue themselves. People who are asleep or drunk can die from carbon monoxide poisoning without ever noticing symptoms. Some key ways to spot when your symptoms could be carbon monoxide poisoning and not the flu are:

  • Everyone in the house, including pets, “gets sick” all at once
  • You feel better when you are outside or out of the house
  • Your symptoms are worse when using equipment that burns fuel
  • You do not have body aches, a fever, or swollen lymph nodes

What Causes Carbon Monoxide Poisoning?

Carbon monoxide poisoning works in two main ways: it prevents your body from taking in oxygen and decreases your ability to use oxygen. 

When carbon monoxide is breathed in, it binds to hemoglobin, the protein responsible for transporting oxygen throughout your body. CO binds to hemoglobin easier than oxygen, so even though you may still be breathing in oxygen too, it is not getting into your blood because CO hitches a ride first. Some carbon monoxide is “extravascular” meaning it is found in tissues outside of your veins. Extravascular CO attaches to some molecules that help your body use oxygen and prevent them from working.

There is research that carbon monoxide poisoning can damage parts of the brain in ways beyond depriving them of oxygen, but this is not well understood yet.

Carbon monoxide is found in exhaust from any engine that burns fuel like cars, generators, and furnaces. Even wood fires produce some. Poisoning becomes possible when fumes from these sources build up and cannot escape with proper ventilation. For example, carbon monoxide could build up to dangerous levels if you left your car running to “warm up” but the garage door was closed. Another way could be that you were burning fire in your fireplace but the flue of your chimney was blocked.

How Is Carbon Monoxide Poisoning Diagnosed?

A healthcare provider will look for three key things before diagnosing you with carbon monoxide poisoning:

  • Symptoms that align with known features of carbon monoxide poisoning
  • Known or suspected exposure to CO
  • Elevated carboxyhemoglobin (COHb) (which is what hemoglobin is called when it is bound to carbon monoxide molecules) levels in the blood

A provider can usually identify the first two pieces quickly by asking you a few quick questions. Measuring COHb levels can be determined by testing a blood sample. While increased COHb levels do indicate carbon monoxide exposure, they cannot accurately tell the severity of the poisoning.

Once you have been diagnosed with carbon monoxide poisoning, there are a few other tests your provider may run. Carbon monoxide poisoning is known to damage heart muscle tissue. You may receive an electrocardiogram (ECG) and have blood tests done that could indicate injury to your heart.


The first thing to do if you suspect you may have been exposed to carbon monoxide is to get to fresh air. If your symptoms are mild or you are unsure if what you are experiencing is carbon monoxide poisoning, you can call the Poison Help Line at 1 (800) 222-1222 for assistance. However, if you or someone you are with is having difficulty breathing, confusion, fainting, or seizures, call 911.

In a hospital setting, the first line of treatment is typically high-flow oxygen through a nonrebreathing facemask. This type of face mask allows you to breathe in much more oxygen than a nasal cannula or regular face mask. It prevents you from breathing ambient air, or breathing in the air you have exhaled. High-flow oxygen treatment is used because it eliminates CO in your blood quicker than breathing in oxygen from the air. It is unclear if high-flow oxygen reduces the likelihood of developing DNS.

Hyperbaric oxygen therapy (HBOT) may also be used in special cases. In HBOT, you are placed in a chamber pressurized several times greater than the normal air, allowing your lungs to take in more oxygen. There are not currently widely accepted guidelines for when to use HBOT, but often it is used for people who:

  • Are unconscious
  • Have heart damage due to CO
  • Have neurological deficits such as confusion or loss of function
  • Have a high concentration of COHb in the blood
  • Are pregnant

Several studies have suggested that using HBOT can reduce deaths and the onset of DNS in people with carbon monoxide poisoning, but more research is still needed.


While carbon monoxide poisoning can be deadly, it is also preventable. The following are some steps to take to keep you and your loved ones safe:

  • Install carbon monoxide alarms in your home and keep them in good condition
  • Know the different symptoms of carbon monoxide poisoning and be alert to exposure risks
  • Make sure all fuel-burning devices are well-vented and well maintained
  • Never leave a car or motor running in an enclosed space like a garage
  • Never run a gas-powered engine within 20 feet of an open window, door, or vent

Comorbid Conditions

People with carbon monoxide poisoning may also receive treatment for cyanide poisoning. Fires can lead to both carbon monoxide and cyanide poisoning and can look similar to each other, so providers may treat as if the patient has both until one or the other can be ruled out. Cyanide poisoning is treated by giving a medication called hydroxocobalamin. This may be given in an ambulance by emergency medical service (EMS) workers or at the emergency department.

Living with Carbon Monoxide Poisoning

Many people who experience carbon monoxide poisoning, especially those with mild symptoms, have no long-lasting effects. The most common lasting effects are seen in those who sustain heart and brain damage. People who had moderate to severe poisoning that resulted in heart damage were found to be three times more likely to die than non-poisoned individuals. 

Those with DNS may also experience lasting effects. Symptoms can take years to resolve and persist in up to 40% of people. Through working together with your healthcare provider you may be able to find treatment or therapy that improves or even resolves your symptoms.

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9 Sources
Health.com 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.
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