Carbon monoxide (CO) is a colorless, odorless, and poisonous gas. It is a product of incomplete combustion and is often found in the exhaust of vehicles and other fuel-burning appliances. Carbon monoxide can also be produced by natural sources, such as volcanoes and forest fires.
Carbon monoxide is a dangerous gas because it can cause serious health problems, including death. Even low levels of carbon monoxide can cause headaches, nausea, dizziness, and fatigue. High levels of carbon monoxide can cause loss of consciousness, coma, and death.