Cardiovascular System

Blood Vessels

Why does blood in the veins look blue?

Since venous blood is oxygen-poor blood, it is not as bright red as arterial blood. It appears as a deep, dark-red, almost purplish color. Seeing “blue blood” in veins through the skin is a combination of light passing through the skin and the oxygen-poor blood.


This is a web preview of the "The Handy Anatomy Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App