Carbon Monoxide Poisoning

Written by Shawna Seed
Medically Reviewed by Shruthi N, MD on November 14, 2024
8 min read

Carbon monoxide (CO) is a gas that you can't smell, taste, or see. It's produced from burning fuels, including natural gas, coal, kerosene, wood, propane, and oil, and is present in engine exhaust. When this gas is present in large amounts, especially in confined spaces, carbon monoxide replaces the oxygen in your red blood cells, which leads to carbon monoxide poisoning. Carbon monoxide poisoning can cause serious bodily harm or even death.

Carbon monoxide vs. carbon dioxide

Carbon dioxide (CO2) occurs naturally in soil and the atmosphere and also is produced by burning fossil fuels. At room temperature, it's a gas with no taste or smell. CO2 can also be found in solid form, commonly known as dry ice. Humans naturally breathe in some carbon dioxide that's in the atmosphere. The functioning cells in your body also create carbon dioxide, and you breathe it out when you exhale.

CO2 is used in fire extinguishers as well as in some laboratories. Concerts and theater productions sometimes use dry ice for special effects. If there's a high amount present in the soil, CO2 can seep into houses. It also can build up when there are a lot of people in a poorly ventilated space. If you're exposed to too much CO2, you might experience health effects. They include:

  • Headache
  • Dizziness
  • Tiredness
  • Restlessness
  • Tingling in your limbs 
  • Sweating 
  • Fast heart rate
  • High blood pressure
  • Coma

What does carbon monoxide smell like?

Carbon monoxide itself has no odor. But it's often mixed with other gases that do smell. What you may think of as the smell of carbon monoxide is actually those other gasses. Car exhaust is one example.

Carbon monoxide levels

A carbon monoxide (CO) blood test shows how much CO is present in your blood. The test measures carboxyhemoglobin, which is produced when your blood mixes with carbon monoxide. Interpreting your test results depends on your gender, age, medical history, and other factors. Your doctor will be able to explain them to you.

Normal ranges (the percentage of CO in your blood):

  • Newborns: 10%-12%
  • Nonsmoking adults: less than 2%
  • Smoking adults: 4%-5%
  • Heavy smoking adults (more than two packs per day): 6%-8%

Higher levels can mean carbon monoxide illness or poisoning.

Carbon monoxide poisoning and pulse oximetry

Pulse oximeters are electronic devices used to measure the amount of oxygen in your blood. Typically, they clip onto your fingertip and give out a reading. Research suggests that pulse oximeters don't give accurate readings for people who have been exposed to carbon monoxide.

In well-ventilated spaces, carbon monoxide isn't usually a cause for concern. When CO is present in large amounts in relatively airtight spaces, it can build up and become dangerous quickly.

Carbon monoxide poisoning

Indoor garages can be particularly dangerous. Don't leave your car running in the garage, even if the garage door is fully open.

Other potential sources of dangerous carbon monoxide emissions include:

  • Faulty gas stoves and appliances such as clothes dryers, space heaters, or fireplaces
  • Wood-burning fireplaces
  • Faulty water heaters
  • Old or faulty furnaces that burn gas, oil, coal, or wood
  • Clogged chimneys
  • Outdoor fuel-burning or gas-powered appliances used indoors
  • Fire

Open air carbon monoxide poisoning

Outdoor activities can create carbon monoxide hazards. Be alert for CO poisoning when you're around: 

  • Outdoor grills
  • Lawn equipment that burns fuel
  • Torches and lanterns
  • Campfires
  • Camp stoves and heaters 
  • Boats
  • Recreational vehicles, such as RVs and ATVs

How long does carbon monoxide poisoning take?

If you're exposed to low levels, it can take up to two hours to show symptoms of carbon monoxide poisoning. At higher levels, the process can take about five minutes.

If you inhale too much carbon monoxide, it builds up in your bloodstream, replacing the oxygen that belongs there. When your heart, brain, or other vital organs are deprived of that oxygen, you’re in trouble.

If this dangerous gas is getting into your system, you might:

  • Feel short of breath
  • Get dizzy
  • Become nauseated
  • Get a headache
  • Feel confused

Carbon monoxide is especially dangerous for infants, those who are pregnant, and people with ailments such as emphysema (which damages the air sacs in your lungs), asthma, or heart disease. Smaller amounts of the fumes can hurt them.

Long-term effects of carbon monoxide poisoning

It's critical to treat carbon monoxide poisoning quickly. Timely treatment may reverse harmful side effects. Depending on how long you were exposed and how much carbon monoxide you took in, you may have long-term health issues, such as:

Carbon monoxide poisoning can affect anyone. However, the risks are higher for certain people. They include: 

  • Those who are pregnant and their fetuses
  • Babies 
  • Smokers
  • Those who live at high altitudes
  • People older than 65
  • Those with chronic heart or breathing issues
  • People with anemia

Certain jobs raise your risk, too. Among them are:

  • Firefighter
  • Mechanic
  • Welder
  • Driver

Pets may be the first in your household to show signs of CO poisoning.

Get the person to fresh air

  • Move the person away from the area exposed to carbon monoxide.
  • If the person is unconscious, check for injuries before moving.
  • Turn off the source of carbon monoxide if you can do so safely.

Call 911

Begin cardiopulmonary resuscitation (CPR) if necessary

If the person is unresponsive, breathing abnormally, or not breathing:

  • Perform CPR for one minute before calling 911 if you are alone. Otherwise, have someone else call and begin CPR.
  • For a child, start CPR for children.
  • Continue CPR until the person begins breathing or emergency help arrives.

Carbon monoxide poisoning is treated with 100% oxygen to reintroduce oxygen into your blood cells. Depending on the severity of your exposure, the oxygen is delivered in different ways.

  • Mild poisoning is treated with oxygen delivered by a mask.
  • Severe carbon monoxide poisoning may require placing the person in a full-body, high-pressure chamber to help force oxygen into the body.

How long does carbon monoxide poisoning last?

With mild exposure, the effects may begin to wear off as soon as you inhale fresh air or pure oxygen. It may take up to a day for the carbon monoxide to leave your body completely. You might still feel symptoms until it clears or for up to two weeks after your carbon monoxide poisoning.

When you buy appliances that burn fuel, look for the seal of a testing agency such as UL. In your home, any equipment should be installed with vents running outdoors.

Here are more tips:

Maintenance. Have a qualified technician inspect your heating system, water heater, and any other fuel-burning appliances every year. If you have a fireplace, ensure that the chimney is examined regularly.

Emergency generators. Don’t use them in your garage or basement. Put them outside the house at least 20 feet from windows or doors.

Charcoal grills and portable camp stoves. Use them only outdoors.

Space heaters. Use them only when someone is awake to keep an eye on them; make sure there is some airflow in and out of the room. Don’t try to use a gas oven for heat.

Vehicles. Have your car or truck’s exhaust system checked each year. If your garage is attached to your home, don’t leave a vehicle running there. Even with the garage door open, the fumes can seep inside the house. If your vehicle has a tailgate, be sure to open windows anytime you drive with the tailgate down. If you don’t, carbon monoxide can be sucked into the vehicle.

Carbon monoxide detector

The U.S. Consumer Product Safety Commission recommends installing carbon monoxide detectors on every level of your home.

These detectors are available at hardware stores and other retailers. Buy alarms that are certified by a testing laboratory. The alarms can be battery-powered or hardwired. Plug-in and freestanding CO detectors are also available.

Always follow the instructions about installation and change the batteries twice a year when the time changes.

Here are a few other guidelines:

  • If possible, place CO detectors outside each sleeping area.
  • Test the alarms once a month. Some alarms also give off audible signals on their own if the battery runs low or if they break down.
  • If you have multiple alarms, connect them. That way, if one detects trouble, they all go off.
  • Ask your fire department for the contact number so that you can call if the alarm goes off.
  • Don't "borrow" batteries from your CO detector; keep it functioning.
  • If you have a boat or motor home, make sure detectors are also available there.
  • Consider portable CO detector options for when you travel.

Signs something is wrong

By keeping your eyes open, you may spot signs that appliances are out of whack or something else is wrong. A few warning signals include:

  • Soot falling from fireplaces or appliances
  • Rust or water streaks on vents
  • Loose or disconnected vent pipes
  • Moisture inside windows
  • Cracked or crumbling masonry on a chimney

If you see any of these, have a trained technician check them out and fix any issues promptly.

Carbon monoxide (CO) is a clear gas with no smell or taste. If you're exposed to too much CO, you may have symptoms such as headache and dizziness. Higher levels of exposure can lead to serious health problems and even death. The best way to avoid carbon monoxide poisoning is to be careful around sources of CO, such as car engines and faulty furnaces and appliances. Don't run heat sources and machines that are meant for outdoor use inside. If you suspect CO poisoning, move the person to fresh air right away. You may need to call 911 and begin CPR. Carbon monoxide detectors can help keep you and your family safe. 

Will opening a window help with carbon monoxide?

Opening a window will let in fresh air, but it's just one step. If you know the source of the CO, turn it off if you can. You should move outside as soon as possible. Don't go back inside until professionals tell you it's safe to do so. 

How do you detect carbon monoxide without a detector?

Because CO has no smell or taste, you can't really know it's there without a detector. However, you can look for signs such as soot falling out of appliances or fireplaces, damaged chimneys, rusty streaks on appliances, loose vent pipes, or moisture building up inside windows.

What appliances leak carbon monoxide?

Household items that can leak CO include: 

  • Fireplaces, whether wood-burning or gas
  • Clothes dryers
  • Furnaces
  • Water heaters
  • Gas stoves and ovens
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