• Question: is it true that your blood is blue but when it hits oxygen it turns red? if so why?

    Asked by ellie science to Rob on 12 Jun 2016.
    • Photo: Rob Stanley

      Rob Stanley answered on 12 Jun 2016:

      No that isn’t true!

      Blood that is oxygenated does have a different colour to blood that isn’t carrying oxygen, but these are only different shades of red! The colour change is caused by the protein haemoglobin, which changes colour when it has oxygen attached (from dark red to bright red).

      A device called a pulse oximeter is still able to use this difference in colour to find out how much oxygen is in your blood.

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