why can you sometimes see your viens whan hey are under your skin

Question: why can you sometimes see your viens whan hey are under your skin
- Keywords:
  cardiovascular,
  human body,
  skin,
  vein
Asked by gristh10 to Anna, Jonathan, Samantha, Sam on 30 Jun 2012.
- Angharad Davies answered on 30 Jun 2012:
  
  Your veins are full of blood. If you get warm, from the weather or from exercising, your body gets rid of the extra heat by sending more blood to near the surface of the skin, so the heat from the blood can escape into the air. So when you’re too hot, there’s more blood in the veins near the skin surface and they look bigger and stand out under your skin.
  
  If you’re very cold, the body tries to keep heat in and sends less blood to the skin, so your veins look smaller and you can’t see them as well.
- Jonathan Kay answered on 2 Jul 2012:
  
  My laboratory receives thousands of blood specimens every day. When you take blood it’s often better to use a vein you can feel rather than one you can see.
  
  You can read lots about this at http://www.labtestsonline.org.uk/lab/samples/
  
  Have you ever had a specimen of blood collected from you?
- Sam Chilka answered on 4 Jul 2012:
  
  I agree with what Angharad said. Many large veins are near the surface of the skin, and because they are usually full of blood, they bulge out and you can see them. Blood which is high in oxygen is bright red. Veins carry blood which is relatatively low in oxygen – so it is usually much darker in colour. That is why veins you can see near the skin often appear blue in colour.
- Samantha Weaver answered on 4 Jul 2012:
  
  The various conditions in which cause veins to be more visible can include thinning of the skin (a side effect of oral and inhaled steroids), anaemia, low body fat, increased blood circulation, temperature change, and sudden weight loss.