What Does Carbon Monoxide Smell Like?
It does not smell like anything. The CDC describes carbon monoxide, or CO, as an odorless, colorless gas that kills without warning, claiming the lives of hundreds of people every year and making thousands more ill. The EPA says that because it is impossible to see, taste or smell the fumes, CO can kill you before you are aware it is in your home. A rotten egg smell is a separate warning. Connecticut's utility regulator notes that natural gas has no odor of its own and that gas companies add a chemical called mercaptan to give it that smell.
Because you cannot sense CO, symptoms are often the first sign. The CDC says the most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, and that they are often described as flu-like.
Detectors are the protection. The CDC advises installing battery-operated or battery back-up CO detectors near every sleeping area in the home, checking the batteries when you change your clocks each spring and fall, and replacing a detector following the manufacturer's instructions or every 5 years. The EPA notes that the Consumer Product Safety Commission recommends CO alarms on each level of every home, outside each sleeping area.
Sources checked September 15, 2026. Every point below links the page it came from.
The sources behind this answer
- Government sourceThe CDC describes carbon monoxide as an odorless, colorless gas that kills without warning and says it claims the lives of hundreds of people every year and makes thousands more ill. CDC ↗
- Government sourceThe CDC says the most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as flu-like. CDC ↗
- Government sourceThe CDC advises installing battery-operated or battery back-up CO detectors near every sleeping area and checking their batteries when you change your clocks each spring and fall. CDC ↗
- Government sourceThe CDC says to replace a CO detector following the manufacturer's instructions or every 5 years. CDC ↗
- Government sourceThe EPA says that because it is impossible to see, taste or smell carbon monoxide fumes, CO can kill you before you are aware it is in your home. US EPA ↗
- Government sourceThe EPA says the Consumer Product Safety Commission recommends that every home have carbon monoxide alarms on each level outside each sleeping area. US EPA ↗
- Government sourceConnecticut's Public Utilities Regulatory Authority says natural gas has no odor and gas companies add a chemical called mercaptan to give it its distinctive rotten egg smell. Connecticut Public Utilities Regulatory Authority ↗
Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.