Why does abnormal oxygen saturation cause you to look blue?

Abnormal oxygen saturation, particularly low oxygen levels, can cause a bluish discoloration of the skin and mucous membranes, a condition known as cyanosis. Here's why:

Hemoglobin: Hemoglobin is a protein in red blood cells that carries oxygen throughout the body. When hemoglobin is saturated with oxygen, it appears bright red. However, when the oxygen levels in the blood are low, hemoglobin becomes desaturated and appears bluish.

Deoxygenated Hemoglobin: When hemoglobin loses its oxygen, it changes its molecular structure and absorbs more blue and violet light. As a result, the skin and mucous membranes take on a bluish hue.

Oxygen Saturation Levels: Normally, the oxygen saturation in arterial blood, measured by pulse oximetry, should be around 95% or higher. When oxygen saturation levels drop below 85%, cyanosis can become noticeable.

Cyanosis can be a sign of various underlying medical conditions that affect oxygen transport or utilization, such as respiratory disorders (e.g., asthma, pneumonia), cardiovascular issues (e.g., heart failure), or certain blood disorders (e.g., methemoglobinemia). It's important to seek medical attention if you notice persistent cyanosis or bluish discoloration of your skin or lips.