This is the question that kept me up at night.
Your blood is red. Bright red when it’s oxygenated (flowing away from your heart in arteries). Darker, maroon red when it’s deoxygenated (flowing back toward your heart in veins). So why in the world do veins look blue or green through your skin?
The answer is light, not blood.
Your skin scatters light. Red light penetrates deeper into your tissues, where it’s absorbed by the blood in your veins. Blue light doesn’t penetrate as deeply—it’s reflected back to your eye. So what you see is the blue light bouncing off your skin, not the actual color of your blood.
That’s why veins look bluish or greenish depending on your skin tone, the depth of the vein, and the lighting. It’s an optical illusion. A fascinating, harmless optical illusion.
Normal (Non-Dangerous) Causes of Visible Veins
Let me put your mind at ease. Most visible veins are not a medical problem. Here’s why yours might be showing.
