Why Is Blood Red?
Aug 27, 2025
Scraped knees, bloody noses, cuts—sometimes in our fallen world we get injured, and some of those injuries cause us to bleed.
But have you ever wondered why your blood is red and not blue or green or purple? To find out the answer, we first need to talk about light waves.
Light travels from the sun in colorful waves—red, orange, yellow, green, blue, indigo, and violet. Each wave of light is a different length. Blue light has the shortest wavelength, meaning it travels in short, choppy waves. Red light has the longest wavelength.
The electromagnetic spectrum, which shows the wavelengths of visible light. Credit: Hanacek/NIST
Blood contains hemoglobin (hee-muh-glow-bin), a protein that is found in red blood cells and transports oxygen throughout the body. Hemoglobin contains iron, which absorbs red light waves and reflects it back to our eyes. The iron is what gives our blood its red color.
If Blood Is Red, Why Do Our Veins Look Blue?
You’ve probably wondered why your blood looks blue in your veins but red when you are bleeding. Some people say that your blood is blue when it is inside your body, but that’s not true. Actually, the color of your veins has to do with how light waves interact with your skin.
Red light is better at getting through the tissues in your skin because it has a longer wavelength. The red light waves seep deeper into your skin and are absorbed by hemoglobin. Since blue light has a short wavelength, it doesn’t get absorbed into your skin as far. Instead, it reaches your veins and is reflected back to your eyes, making your veins appear blue or green.
Our Brilliant Blood
The color is just one cool thing about blood! Blood brings oxygen from your lungs and carries nutrients from your stomach to the rest of your body. Your blood also contains white blood cells that fight off germs. And while it’s zipping through your veins, blood keeps your body warm.
With all these brilliant jobs, your blood never could have just evolved over time. From head to toe, blood keeps all your body systems functioning the way they were designed to by our creative and caring God on day six of creation week just 6,000 years ago.
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