Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion of carbon-containing materials. It has a strong affinity for hemoglobin in red blood cells, forming carboxyhemoglobin which prevents oxygen from being delivered to tissues. Symptoms of CO poisoning range from headache and dizziness with 10-20% carboxyhemoglobin, to confusion, loss of consciousness, and death with levels over 40%. Chronic low-level exposure can cause neurological and psychological effects. Treatment involves removing the victim to fresh air with supplemental oxygen. High CO levels or symptoms require hyperbaric oxygen therapy. CO poisoning can be accidental or intentional via suicide or homicide.