Daily BulletinDaily Bulletin

The Conversation

  • Written by David Irving, Adjunct Professor, University of Technology Sydney

This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au

I’ve always wondered why our veins are blue, when blood is red? - Alexandra, 28, Melbourne

Blood is red, and a surgeon will tell you our veins too are red, they only look blue when we see them through our skin. But why?

The answer depends on a number of things, including how your eyes perceive colour, how light behaves when it contacts your body, and the special properties of blood.

Light travels in peaks and troughs. And the distance between each trough is called a wavelength. Different colours of light have waves of different lengths. Red light has a long wavelength (about 700 nanometres), violet light has a short wavelength (about 400 nanometres), and the rest of the spectrum is spread out in between.

I've always wondered: why do our veins look blue when our blood is red?

We see something as a particular colour when light of that colour hits our eyes –either directly from a light source or reflected from a surface.

To understand what colour our veins appear, we need to think about what happens to different wavelengths of light when they hit our skin, how far they can travel through our skin, and what happens when they get to our veins.

Read more - Curious Kids: Why are rainbows round?

The light that hits our skin during the day is basically white, which is a mixture of all the visible wavelengths. But to explain why our veins look blue, we will look at just the red and blue ends of the spectrum.

Red light has a long wavelength – and this means it is less likely to be deflected by materials and can more easily travel through. Red light can travel pretty well through the skin and body tissues, reaching up to 5-10mm below the skin, which is where many veins are.

When it gets to the veins, the red light is absorbed by the haemoglobin (the protein that makes our blood red). You can demonstrate this to yourself. If you shine a red light on your arm, you will see some red light reflected back, and dark lines where the veins are, as the red light is absorbed by the haemoglobin.

Read more - Explainer: what’s actually in our blood?

Red light makes our veins appear as dark lines.

This phenomenon is actually used to help medical personnel find veins to take blood – by shining red, and sometimes infrared (which is an even longer wavelength) light on the arm.

Blue light has a short wavelength (about 475 nanometres), and is scattered or deflected much more easily than red light. Because it’s easily scattered it doesn’t penetrate so far into the skin (only a fraction of a millimetre). When blue light hits the skin, it’s mostly deflected back.

If you shine a blue light on your skin, what you see is basically blue skin, and veins are hard to find. You may have seen blue light used in spaces such as public bathrooms to discourage intravenous drug use.

I've always wondered: why do our veins look blue when our blood is red? Blue lighting is used in some spaces to discourage intravenous drug use as it makes it harder to find veins. Wikimedia Commons

So, now imagine the red light and the blue light shining on your skin at once, as happens when you are under white light. You will have a mixture of red, blue and other colours reflected back where there are no veins. Where there are veins, you will see relatively less red, and relatively more blue compared to the surrounding skin.

This means your veins will appear blue compared to the rest of your skin.

I've always wondered: why do our veins look blue when our blood is red? The Conversation, CC BY-ND Interestingly, the effect varies depending on how deep the vein is, and also on how thick the vein is. Very narrow veins close to the surface, such as the capillary bed, will not appear blue. Blue veins appear more prominent in very pale skinned people, and this may have given rise to the expression “blue blood” for European nobility in the 19th century. These people were untanned from manual labour, and so their veins appeared blue under the skin. With thanks to Science Writer at the Australian Red Cross Blood Service Alison Gould. * Email your question to alwayswondered@theconversation.edu.au * Tell us on Twitter by tagging @ConversationEDU with the hashtag #alwayswondered, or * Tell us on Facebook

Authors: David Irving, Adjunct Professor, University of Technology Sydney

Read more http://theconversation.com/ive-always-wondered-why-do-our-veins-look-blue-when-our-blood-is-red-83143

Trauma, resilience, sex and art: your guide to the 2020 Miles Franklin shortlist

arrow_forward

Raising a Child with a Disability? Learn How the NDIS Can Help

arrow_forward

The Conversation
INTERWEBS DIGITAL AGENCY

Politics

Prime Minister Interview with Ben Fordham, 2GB

FORDHAM: Thank you very much for talking to us. I know it's a difficult day for all of those Qantas workers. Look, they want to know in the short term, are you going to extend JobKeeper?   PRI...

Scott Morrison - avatar Scott Morrison

Prime Minister Scott Morrison interview with Neil Mitchell

NEIL MITCHELL: Prime minister, good morning.    PRIME MINISTER: Good morning, how are you?   MICHELL: I’m okay, a bit to get to I apologise, we haven't spoken for a while and I want to get t...

Scott Morrison - avatar Scott Morrison

Prime Minister Interview with Ben Fordham

PRIME MINISTER: I've always found that this issue on funerals has been the hardest decision that was taken and the most heartbreaking and of all the letters and, you know, there's been over 100...

Scott Morrison - avatar Scott Morrison

Business News

Understanding Your NextGen EHR System and Features

NextGen EHR (Electronic Health Records) systems can be rather confusing. However, they can offer the most powerful features and provide some of the most powerful solutions for your business’s EHR ne...

Rebecca Stuart - avatar Rebecca Stuart

SEO In A Time of COVID-19: A Life-Saver

The coronavirus pandemic has brought about a lot of uncertainty for everyone across the world. It has had one of the most devastating impacts on the day-to-day lives of many including business o...

a Guest Writer - avatar a Guest Writer

5 Ways Risk Management Software Can Help Your Business

No business is averse to risks. Nobody can predict the future or even plan what direction a business is going to take with 100% accuracy. For this reason, to avoid issues or minimise risks, some for...

News Company - avatar News Company



News Company Media Core

Content & Technology Connecting Global Audiences

More Information - Less Opinion