As title suggests. Thanks

If you can't breathe, then you have high concentration of deoxygenated blood. Deoxygenated blood is blue/purple and causes the blue coloration of the skin.

Deoxygenated blood is not blue, it's dark red. If you've ever given blood, you can see deoxygenated blood flowing along the tube as it is taken venously. It looks like red wine.

 

Oxygenated blood is bright scarlet, so your answer could still be correct, in that because the scarlet colour of oxygenated blood contributes much of the hue of normal skin colour, when the blood is less oxygenated the skin is less bright red. Cyanosis is not people actually being blue, they just appear bluish due to the relative colour difference between normal skin tone and cyanosis. Here's a paper which attempts to explain why veins appear blue (PDF); the same principle applies to cyanosis.

Edited February 14, 201114 yr by Blahah

Thanks for the reply but I think people with ashtma have less problem in inhaltion, but more problem in exhalation. So it is the resultant increase in carbon dioxide shifting the hameoglobin dissociation curve to the right that causes this. I posted this topic to clarify?