Carbon (II) oxide is considered dangerous if inhaled mainly because it

Carbon (II) oxide, also known as carbon monoxide (CO), is considered dangerous if inhaled because it competes with oxygen in the blood. Hemoglobin, which is responsible for carrying oxygen throughout the body, has a much greater affinity for CO than it does for oxygen. This means that when CO is inhaled, it binds to hemoglobin instead of oxygen, reducing the amount of oxygen that can be carried in the blood. This can lead to hypoxia, a condition in which the body is deprived of adequate oxygen, and can result in symptoms such as headache, dizziness, weakness, and even death.