As a medical expert with a focus on anatomy and physiology, I can explain why blood may appear blue when viewed through the skin, particularly in veins.

The color of blood as we perceive it is influenced by the way light interacts with the skin and the blood itself. Oxygenated blood is bright red because it contains oxygen, which is transported by hemoglobin. Deoxygenated blood, which has released oxygen to the tissues, is darker and can appear more blue or purple.

When we look at veins, especially those close to the surface of the skin, we are not seeing the blood directly. Instead, we are seeing the blood through a layer of skin and tissue. The skin scatters light, which can make the deoxygenated blood appear more blue than it actually is. This is due to a phenomenon known as selective absorption. The skin and tissue absorb more red light, which is why the remaining light that is transmitted back to our eyes is more blue in color.

Additionally, the thickness and color of the skin can also affect the perception of blood color. Thicker or darker skin may absorb more red light, making the veins appear more blue.

In summary, the blue color of veins is not because the blood is actually blue but because of the way our skin and the surrounding tissues filter the light that passes through them, which changes the color of the light that reaches our eyes.

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Since arteries carry oxygen-rich blood away from the heart and veins carry oxygen-depleted blood back to the heart, some people believe that veins appear blue because blood without oxygen is blue. But it's not true! Blood is always red. ... Blue light does not penetrate human tissue as deeply as red light does.read more >>