If the blood is red, why are the veins blue?

Although they say there are people who have blue blood running through their veins, the truth is that human blood is invariably red. But have you noticed that white-skinned people have bluish-veins?

Human blood is not blue. Never. Never.

Typically, medical and biology textbooks and books illustrate venous blood as blue. Thus, many came to believe that this would be the reason why the veins have a tone of this color.

This blood has low oxygen concentrations and circulates from our organs to the heart, from where it is pumped to the lungs through the pulmonary arteries. The blood is then oxygenated and returns the O ₂ to the organs so that they can function properly and is then called arterial.

In addition, the red color of “liquid” comes from a mixture composed of hemoglobin, iron and molecular oxygen.

But ... why blue?

The explanation is up to the physics. Simply put, the color we see is the way our eyes interpret the light reflected by the objects we observe. Absorbed the light, these organs see the tone - or wavelength - that the object "rejects". Thus, the white color results from the absorption of all colors, while black is the product of the absence of all of them. So we see blood as red because that is the wavelength that the substance reflects. But when is it under the skin?

White skin cannot absorb much light and reflects almost all light rays. This is why it seems to be clearer. Blood - outside the veins - can absorb all wavelengths except red, which is the color it reflects. When it is inside the veins, the blue wavelength cannot penetrate like red, reflecting back so that our eyes can interpret as the bluish hue we see.