why do your fingertips turn a tinge of blue when they are cold?

Question: why do your fingertips turn a tinge of blue when they are cold?
- Keywords:
  blue,
  cold,
  fingertip
Asked by 526curm33 to Matthew on 5 Mar 2018.
- Matthew Beaney answered on 5 Mar 2018:
  
  When blood has a lower level of oxygen and becomes a darker red, more blue light is reflected, making the skin appear to have a blue tint.

Matthew commented on 5 Mar 2018:

Cold temperatures cause blood vessel narrowing in the fingertips so less oxygenated blood gets through.

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- BookynessClarkeEllen&Noni commented on 5 Mar 2018:
  
  WOW i never knew that! thank you so much booky (pronounced boo and key)
  
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423curm29 commented on 10 Mar 2018:

Why are you talking about your fingers terning blue when they are cold?

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Question: why do your fingertips turn a tinge of blue when they are cold?