What's the reason the skin looks blue when having cyanosis? What's the relationship between lack of oxygen of the bluish appearance?

  • Have you thought about the coloring of arterial and venous blood?
    – Bryan Krause
    Commented Jul 5, 2020 at 1:09
  • Yes, and it still doesn't explain to me the bluish colour. (lack of red doesn't mean blue) Commented Jul 5, 2020 at 1:35
  • What color is venous blood?
    – Bryan Krause
    Commented Jul 5, 2020 at 2:16
  • Darker red than the arterial one. Commented Jul 5, 2020 at 2:21
  • 1
    @UbiquitousStudent No, it's not simply darker red. It has a purplish hue, and to make purple you mix which two colors?
    – Carey Gregory
    Commented Jul 5, 2020 at 4:06

1 Answer 1


The skin of a caucasian-skinned person with cyanosis is described as bluish, but it is still more reddish than blue. The bluish jumps out at us in comparison with healthy well-oxygenated blood.

The colors we see are the product of the incoming light, and the proportion of the wavelengths that are absorbed, scattered, or reflected. Because skin and arteries/capillaries/veins are translucent, there's normally quite a bit of red light scattering and reflection going on. However when looking at veins or cyanotic skin, there's less reflection of the red wavelengths, and the skin looks darker and bluer than we're used to.

If you look at a photograph of someone with Raynaud's or cyanotic hands, you'll see that there's still quite a bit of red!

  • This may partly explain why we see different colors, but it doesn't answer the question of why cyanosis causes those changes to occur.
    – Carey Gregory
    Commented Sep 24, 2020 at 23:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.