Why do people turn purple or blue when they are being suffocated?

The bluish or purplish discoloration of the skin when someone is being suffocated is called cyanosis. It occurs when the blood in the body is not carrying enough oxygen.

Blood is normally red because it carries oxygen-rich red blood cells. When someone is suffocating, their lungs are not able to take in enough oxygen, and the blood that is circulating through the body is not carrying enough oxygen. This oxygen-depleted blood is called deoxygenated blood, and it is darker in color than oxygen-rich blood. As more deoxygenated blood circulates through the body, the skin and mucous membranes start to appear blue or purple.

Cyanosis is a sign of severe hypoxia, which is a lack of oxygen in the tissues. Hypoxia can damage cells and organs, and it can eventually lead to death.