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Carbon Monoxide

Why am I being warned about potential exposure to carbon monoxide?
  • Carbon monoxide (CO) is on the Proposition 65 list for reproductive toxicity.
  • Exposure to high levels of carbon monoxide during pregnancy can affect the baby’s brain development and cause loss of pregnancy.
  • California’s Proposition 65 requires businesses to warn people before exposing them to a significant amount of a chemical listed under Proposition 65 for cancer or reproductive toxicity.
What is carbon monoxide?
  • Carbon monoxide is a colorless, odorless, and poisonous gas.
  • It is formed during the combustion of various fuels, including gasoline, diesel fuel, natural gas, wood, coal, kerosene, and propane, as well as plant-derived substances such as tobacco smoke and cannabis (marijuana) smoke.
  • Carbon monoxide can replace oxygen in the bloodstream. During pregnancy, reduced levels of oxygen in the bloodstream can affect the development of the baby’s brain
How does exposure to carbon monoxide occur?
Carbon monoxide is produced during combustion
People breathe air that contains carbon monoxide

Exposure occurs by breathing air that contains carbon monoxide. Sources include:

  • Cooking and heating appliances that may be incorrectly installed or maintained, or may be inadequately ventilated, such as:
    • Unvented kerosene, gas, and water heaters.
    • Wood stoves.
    • Leaking fireplaces, chimneys, and furnaces.
    • Charcoal and propane equipment that is improperly used indoors, in garages, or in unventilated areas.

Other sources include:

During pregnancy, carbon monoxide can pass from mother to baby.

How can I reduce my exposure to carbon monoxide?
  • Ensure that equipment and appliances that produce carbon monoxide are installed correctly, maintained in good condition, and vented to the outside, whenever possible
  • Install a carbon monoxide alarm in your home, test it frequently, and replace its batteries as recommended.
  • Obtain annual inspections by a trained professional for heating systems and chimneys. Make sure that vent pipes, flues and chimneys are properly connected, cleared of any blockages, properly vented to the outside, and otherwise in good condition.
  • Limit the time you spend in enclosed parking facilities, service stations, and vehicle-repair facilities.
  • Always follow the manufacturer’s instructions for fuel-burning equipment, including propane heaters and stoves. Products designated for outdoor use only should not be used indoors.
  • Never use kerosene heaters, charcoal grills, or barbecues indoors.
  • Do not idle a car in an enclosed garage or shed, even if the door is open to the outside. Carbon monoxide present in motor-vehicle exhaust can build up very quickly in garages, sheds, and the living areas of homes.
  • Never leave any machinery with gasoline-powered engines running in enclosed spaces. This includes lawn mowers, weed trimmers, snow blowers, and chain saws.
  • Never use your gas stove or oven to heat your home.
  • Do not use unvented gas fireplaces.
  • Do not use gasoline-burning appliances in enclosed spaces. For example, do not use gasoline-burning generators or camp stoves in homes, basements, campers, tents, vans, trucks, garages, or mobile homes.
  • Do not smoke. Do not allow children to breathe in tobacco smoke.
For more information:

General Fact Sheets and Resources

Scientific Information on Carbon Monoxide

Proposition 65

Updated February 2025
Fact Sheet - Carbon Monoxide

Related Chemical(s)

Related Product or Place

References
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