Question: why is the blood blue but comes out red

Loan Nguyen answered on 11 Nov 2015:

Hi, This is an interesting question.
From my understanding, human blood is red, both inside the body and when we bleed. I have never been taught at school that our blood is blue.
In text books venous blood is coloured as blue to show that is deoxygenated and blood from the arteries is coloured red to show that it is rich in oxygen. Oxygen is carried by iron in the haemoglobin in our red blood cells. This gives red blood cells their red colour. Venous blood is much darker red than arterial blood, but definitely not blue. The reason our veins look blue through our skin is because the skin reflects light of a certain wavelength which gives the illusion that blood inside our body is blue when in actual fact it is red.

I hope that i have answered your question. Keep asking, it is the best way to learn.

Loan