Carbon monoxide (CO) is a colorless, odorless, and tasteless gas produced by the incomplete burning of carbon-containing fuels like wood, coal, gasoline, or natural gas. This invisible compound results from combustion in devices such as furnaces, stoves, and cars. Often called the “Invisible Killer,” CO represents a serious danger in any enclosed space and is responsible for hundreds of accidental deaths each year, often due to malfunctioning or improperly vented fuel-burning appliances.
The Sensory Reality of Carbon Monoxide
The definitive answer to what carbon monoxide smells like is that it has no odor or taste. This sensory neutrality is precisely what makes CO so lethal, as the human body has no way to sense its presence and a person can be exposed to toxic levels without immediate warning.
Any odor noticed in a home—such as a burning smell, car exhaust, or the faint scent of natural gas—is not carbon monoxide itself. These smells are combustion byproducts or additives, such as the odorant mercaptan added to natural gas to make leaks detectable. Relying on smell to detect a CO leak is a dangerous misconception that often leads to delayed action.
How Carbon Monoxide Harms the Body
Carbon monoxide poisoning hijacks the body’s oxygen transport system. The gas is absorbed through the lungs and quickly enters the bloodstream, where it binds strongly to hemoglobin—the protein in red blood cells responsible for carrying oxygen. CO’s affinity for hemoglobin is approximately 200 to 250 times greater than that of oxygen.
When CO binds, it forms carboxyhemoglobin, which displaces oxygen from the red blood cells. This displacement drastically reduces the blood’s total oxygen-carrying capacity, leading to cellular hypoxia, or oxygen starvation, in vital organs. Furthermore, carboxyhemoglobin causes the remaining oxygen molecules to be held much more tightly. This change prevents oxygen from being released into tissues and organs that need it, rapidly impairing the function of organs with high oxygen demand, most notably the brain and the heart.
Physical Warning Signs of Exposure
Since the gas provides no sensory warning, the first indication of exposure is the onset of physical symptoms as the body suffers from a lack of oxygen. Early, mild symptoms of CO poisoning can easily be mistaken for the flu or a common stomach illness, often leading to misdiagnosis. These initial signs include a headache, general weakness, dizziness, and mild nausea.
As exposure continues and carboxyhemoglobin levels rise, symptoms progress to more severe manifestations. Individuals may experience vomiting, chest pain, shortness of breath, confusion, and a loss of muscle coordination. The most dangerous scenario occurs when a person is exposed while sleeping, as they may lose consciousness and suffer irreversible brain damage or death. If multiple people or pets in the same location experience these symptoms simultaneously, it is a strong indicator of carbon monoxide exposure.
Essential Environmental Detection Methods
Because human senses cannot detect carbon monoxide, technology must serve as the primary warning system. Installing certified carbon monoxide alarms is the most effective way to protect against accidental poisoning. Alarms should be placed on every level of the home, especially near sleeping areas, to ensure occupants are woken by the sound.
Alarms should be situated at least 15 feet away from fuel-burning appliances, such as furnaces and gas stoves, to avoid false alarms from trace amounts of CO produced during normal operation. Regular testing and battery replacement are necessary to ensure the devices remain functional. Common sources of dangerous CO buildup include improperly vented appliances, blocked chimneys, and the use of a portable generator or a car inside an attached garage. If a CO alarm sounds, immediately evacuate the area to fresh air and call emergency services.