Yes, carbon monoxide (CO) is a poisonous gas. CO is produced anytime something is burned. It is one of the leading causes of death in fires. When a person breathes CO, the gas prevents the blood cells from carrying oxygen to the body. Symptoms are caused by poor oxygenation, which often affects the neurologic system (brain and spinal cord) first. There is often confusion, lightheadedness, weakness, reddened skin, and even loss of consciousness or death if the exposure is too strong or too long.