Why are veins blue? We explain

by Corinna

Why veins are blue or look blue even though the blood flowing through them is red is a fascinating question. The phenomenon is easy to explain

Veins are blue: Why this is the case

In order to see things, we need light. When it hits our skin, it penetrates deep into the skin layers. The light rays are absorbed, i.e. reflected or reflected back. Some colors are reflected during this process so that we can see certain colors clearly and others are swallowed up.

  • In the case of skin, the light rays penetrate the skin to different depths. As the blue light is reflected more quickly by the veins or blood vessels, while the red light penetrates deeper and is swallowed, we see the veins, such as the veins, shimmering blue through the skin.
  • With darker skin types or when the skin is tanned, we perceive the blue less strongly. Pale skin, on the other hand, makes the blood vessels appear more clearly blue. This is where the saying that aristocrats have blue blood comes from. Nobles used to spend more time indoors and therefore had paler skin than the rest of the population. Their blood vessels looked bluer
  • In contrast, blood vessels that lie close to the surface of the skin tend to shimmer red through the skin tissue. If light rays hit these blood vessels, they do not penetrate as deeply. The red light is also reflected back and not absorbed
  • This is clearly visible in the facial area. In the case of vascular and connective tissue weakness, vascular dilatation can be seen as slight redness on the nose and cheeks. The small blood vessels also shimmer darker through the skin when the person affected is stressed or excited, their blood pressure rises, the outside temperature fluctuates or they have undergone heavy physical exertion.
  • Conclusion: Red blood flows through the veins just as it does through the arteries. When sunlight hits our skin, the blue light is reflected more strongly by the blood vessels, while red light rays are absorbed. For this reason, veins, for example, appear blue, even if the blood flowing through them is actually red.

Scientific explanation

In the 1990s, a number of experts, including the German physicist Alwin Kienle, Lothar Lilge, Michael S. Patterson, Raimund Hibst and Rudolf Steiner, clearly explained why we see veins shimmering blue through the skin. They took a new look at an old and already frequently discussed question and also published a script on the subject.

  • In an experiment, the researchers show that how we perceive colors depends on four factors. It depends on how the different light waves are scattered and reflected by the skin, how high the oxygen content in the blood is, the structure and properties of the blood vessels and how the observer perceives things visually.
  • Light travels in waves. Red light has a longer wavelength, blue a shorter one. Red light waves therefore penetrate deeper into the skin layers than blue ones. This is why the blood vessels reflect the shorter wavelength, i.e. the blue light – the veins appear blue.
  • The experiment clearly showed that blood vessels must be less than 0.5 mm deep under the skin for them to appear red. This is very clearly visible in the lips
  • Whether the blood in the blood vessels that we see through the skin appears as light or dark red depends on the oxygen content of the blood. Basically, oxygen-rich blood is lighter and oxygen-poor blood is darker

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