Flickr / Andrew Mason

Blood flows through a complex network of veins within our body, carrying nutrients to our organs, fighting off disease, and taking harmful materials to areas where they can be neutralized and disposed of.

Blood is made up of 95% water, which allows it to flow easily between organs.

Blood is made of a complex number of proteins and chemicals. Hemoglobin is the primary thing that gives blood its red color. Hemoglobin combined with oxygen produces a bright red color, the color many of us are used to seeing after suffering a cut or as seen on TV. A popular misconception, spurred by the fact that by looking at your veins, it appears that the blood running through your body is blue. Common reasoning would dictate that blue veins would mean that the liquid flowing through them would also be blue. This however is not the case, as we will see.

An Optical Illusion

The blood within your body is at dark red, and always is. Another thing that perpetrates this myth is the fact that many medical textbooks show both red and blue veins, to differentiate between veins and arteries. The reason your veins show that your blood is blue is nothing but an optical illusion from the light. Due to the way light acts on our skin, and given that only certain kinds of light can really penetrate our skin. Specifically red light goes through skin easier than blue light, red light gets absorbed by our skin, and the blue light is reflected. Therefore the blue light is perceived in our eyes more easily than red, and is the main reason for the perception that “blood is blue” inside our bodies. The veins themselves are of neutral color, and have no effect on the color of blood.

Is blood ever blue?

Many people claim that that blood that has been drained of oxygen maintains a different color, and this is why the blood you donate is a different color than blood from a wound. This kind of deoxygenated blood is known as venous blood, and is probably the closest thing human blood can come to being another color. Nonetheless venous blood usually maintains a maroon, or very deep dark red color. The only time blood may appear even the slightest amount of blue is if the person is a sufferer of sulfhemoglobinemia, a very rare condition which denotes a lack of hemoglobin in the blood, and as such the person may have extremely dark red blood, with a bluish tinge. Mollusks and some arthropods (insects and crabs) have blue blood due to a protein in their blood called “hemocyanin” which lacks any color when not exposed to oxygen, but turns blue when exposed to oxygen. Blood within a human body however, can never be blue under natural circumstances.