Is Blood Ever Blue? Science Teachers Want to Know!

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Once a month I get stuck in a vein, and my blood sucked into a evacuated test tube. Under the circumstance, the color is very much like your Pantone Dark Red.

By Jim Thomerson (not verified) on 01 Sep 2010 #permalink

Shouldn't a chemist somewhere be able to take a drawing of some human blood, add heparin, sequester the oxygen somehow, and give us a picture of oxygenated versus un-oxygenated blood?

This is funny! I've been living under the misconception that blood is in fact a dark purple blue (more purple burgundy?) in the veins but turns red (dark to light depending on the amount of blood) when exposed to air. And the internet has only cemented that notion with all it's danged experts and citations.:P

That's very good. Before I retired from teaching middle school science, kids would always tell me, "my teacher said you can't see blood in your veins without oxygen, so how can you tell it's not blue?" I would say "When I have to give a blood sample, I watch it in the tube. No oxygen, not blue. Try it." Looks to me like your bottom color sample - not blue. Well done.

What Jared said.
The color of the "blood" (or hemolymph) depends on what the heme is binding to.

We dissected Manduca sexta larva (tobacco hornworm) last year and their hemolymph was a bluish green. Although apparently it will dye your hands a dark color if you get it on there and let it sit for a while.

This is like elementary level anatomy info.

Some species of crab have blue or green blood, due to having hemoglobin that's based on copper instead of iron (same thing with Vulcans). (Would it then be cuproglobin?)

Blood is never blue. I have yet to dissect a mammal or non-mammal with blue blood. Sometimes preparers inject cadavers with blue latex to help simplify studying, however naturally it is not possible.

By Phillip T., M.D (not verified) on 25 Oct 2010 #permalink

Blood is never blue. I have yet to dissect a mammal or non-mammal with blue blood. Sometimes preparers inject cadavers with blue latex to help simplify studying, however naturally it is not possible. Crabs have hemolymph not blood

By Phillip T., M.D (not verified) on 25 Oct 2010 #permalink

Hemolymph is found in animals with open circulatory systems(no vessels), blood is found in closed circulatory systems

By Phillip T, M.D (not verified) on 25 Oct 2010 #permalink

Phillip, good point about the hemolymph vs. blood. From now on I will use this tool to bludgeon my detractors such as Jaf who is always trying to show how she is smarter than me.

I cannot believe that people are actually arguing that blood is blue or red. This is very simple, and as someone who diagnoses and treats vein disease I should know, blood is always some type of red. Your veins looks blue under your skin, for the same reasons that the sky looks blue. It is a really cool concept called refraction. When you have your blood drawn for evaluation, we draw it from veins (generally). The blood is actually drawn into a device called a VacuTainer. There is a reason we use the prefix "VACU" and it is due to the fact that we will draw blood in a vacuum tube. The reason to put it into a vacuum is so we can test it as closely to the internal body as possible.

So, when your blood is drawn, and it looks red; it still hasnt event hit O2 yet. Furthermore, to define veins as "deoxygenated" and arteries as "oxygenated" further means that our teachers have zero ability to open a book. Arteries carry blood away from the heart, and in fact the Pulmonary artery (which carries blood from the right ventricle to the lungs to get oxygen) is oxygen starved blood. Further, the Pulmonary Vein is oxygen rich and brings blood to the left atrium to goto the left ventricle and will distribute to the body through the Aortic Valve.

Your veins do not look blue once we open the skin. Arteries and veins alike are white. Arteries are thicker and have pulsitile flow. Veins are thinner and have a more constant flow in a low pressure system.

I have gone into many classrooms, and have realized that many teachers and even medical professionals, are teaching children radical information. Please do some simple research and you will find this true. If you are in a very powerful position of providing knowledge to our future physicians, nurses, educators, legislators, or even grocery worker- give them the correct information.


I have worked in labs for 12 yrs and come across A LOT of blood. And I draw blood and test it. I have never seen blue human blood, EVER. I have seen green blood many times, but this being from specimens taken from dead bodies. The green is along the lines of cooked spinach green to almost brown-- a sludgy green color, not a grass green or pistachio green. It's possible that blood that is contaminated with medications and whatnot may have another color than what it naturally would be.

I have been told by dozens of young patients recently that "blood is blue, right?" or "I was told blood is blue, is the correct?" This while I am drawing them and pointing to them that what is coming from their veins is red. At first I was shocked, and had to question myself and what I've seen and what I've learned. thinking, why are they asking me this in this day and age? Because, it is red, whether it is dark red or light bright red, it's red. RBCs are red. RBCs mixed with plasma, make a red colored liquid. Inside a living being, it is red. If it's put in a tube, spun down and separated, the RBCs are still reddish.

I was taught, that ages ago people had the misconseption that it was blue because it appears to be through the skin. But the truth is, deoxygenated (venous) blood appears as a darker red in humans, oxygenated (arterial) blood is brighter and lighter red. Under the skin, veins appear blue/green, but in fact carry blood that is deep red.

I have to wonder why this sudden belief that blood is blue? Is it easier to teach children that venous blood is blue (even though it's not) and arterial is red? At least they should make it a point to say, blood really isn't blue. If anything, say it's green to brown, but not blue.

I recall a kid in school telling me that venous blood is in fact blue, but as soon as light shines on it it turns red. I asked him how that can possibly have been measured. He didn't speak to me after that.

"This color is 24% red, 2% green, 2% blue, but at a saturation of 92 with a color value of 24 and a hue of 0 degrees. Whatever that means."

RGB (along with a definition of what R, G, and B mean, which depends on your computer monitor's phosphors or LEDs or whatever) is sufficient to specify the color. Saturation, color and hue are a transformation from a color space with cartesian coordinates to one with polar coordinates. Saturation is unevenness of colors: (0,255,0) is saturated green; (0,0,0), (128, 128, 128) (255,255,255) are not saturated at all black, gray, and white. Color value (or brightness) is the mean of R, G, and B. And the hue is some kind of arbitrary angle where 0°, 120°, and 240° are primary colors.

So you don't need HSB, and if the implementation of the hue transformation is wrong, you won't get right results anyway. RGB is (mostly) enough.

By Timberwoof (not verified) on 29 Jun 2011 #permalink

Eric is right, blood is not blue in the body. All blood carries oxygen, venous blood just doesn't carry as much as arterial blood. Actually the erythrocytes carry the oxygen as the hemoglobin in the cell is oxidized (Fe + O2) and the blood cell "rusts" which accounts for the very bright red that you see from a cut.
Veins are "darker" because there is less oxygenated erythrocytes in the blood stream. Anyone who has donated or has had blood drawn has seen the color of this blood.
Venous blood looks blue through the skin due because light must enter the epidermis, then the dermis, and then reflect back out to the surface. The various colors are transmitted/not transmitted and you see a blue shade look at blood through your skin. Remove the skin and veins would look white as it is surrounded by connective tissue. If you could see "into" the vein, the blood would look as it does during a blood draw.
Since veins are very superficial in the arm, it is easy to see the veins.
Try looking at them with a very intense light-say one of those garage halogen lights.
You might see something different.

Believe it or not this is a common misconception, even amongst the highly educated. I myself am a victim of this urban ledge. Granted I grew up in a public school system but an affluent one.

Recently a friend of my brought up the question of venous blood being blue, because to her it seemed stupid that blood would ever be blue. My self & her boyfriend responded (like parrots) what we had been taught in "elementary anatomy" that De-oxidized blood was blue returning to the heart and after leaving the lungs was red (returning to the heart) before it was pumped back out to the body.

We asked more friends, and all reiterated the same story. This is what we had been taught. This is what we had known to be true our entire lives. We are all from different schools, counties, and even states. We have a diverse set of knowledge, and levels of education including, doctorate, masters, BS, BA. Thus began the google search.

My friend found many blog sites (such as this one), yahoo answers (which I noticed was reference here), and so on. However, being that the internet is what it is, you can find any answer you desire without it necessarily being true.

Here I begin to see a problem. I am by no means in the medical field, but I do know how to research. So I began a quest to find the real truth to this.

...drum roll...

Blood is not blue, ever. Bright red to purple blue depending on your of personal perceptions of color. Much as was stated by Greg Laden with the color example. - Nice point, by the way.- However an accumulation of very logical arguments posted on the internet is not enough. I needed an peer-reviewed article. And tah-dah!

A perfect citation supporting that venous/de-oxidized blood is dark red (of sorts), but a test as to the reason why the veins appear blue. I will continue to research and hopefully find other sources, because one article simply is not enough, but it is a start.

I also now need to tell my friend that she was right. Darn.

If anyone finds any good sources, I would love to see them. Thanks.


Thanks for that link! I've seen that (came across it while researching this post). It isn't really about how blood is not blue, but it is very relevant to a likely source (or partial source) of the myth. The other, of course, being the anatomical drawings, which, in turn, almost certainly arise from the bluish nature of veins.

The best myths are highly circular or even spiral like!

im only a highschool student . but I am an A plus student and am extremely interested in the human anatomy and physiology. I had been studying the human body since 7th grade and I've met TONS o people who think blood is blue. which that statement is very false. this article might just be my proof to everyone that blood really isn't blue . thank you so much !

im only a highschool student . but I am an A plus student and am extremely interested in the human anatomy and physiology. I had been studying the human body since 7th grade and I've met TONS o people who think blood is blue. which that statement is very false. this article might just be my proof to everyone that blood really isn't blue . thank you so much !

my FBC test half the tube was filled with blue and the other half with red colour blood opinion was that its normal


Actually, Carbon Dioxide bound Hemoglobin is blue, there just exists no pure Carbon Dioxide bound Hemoglobin in the body, as blood is a complex mixture of many different things, and even de-oxygenated blood still contains oxygen in smaller amounts. The blue Carbon dioxide bound Hemoglobin mixed with the regular blood coloured Oxygen bound Hemoglobin, makes the dark colour we are referring to. If you want to take things even further, one could argue that blood is neither red nor blue inside the body because for one, there is little to no light inside the body, and Two, there is nobody to see the colour. "Colour" is the perception of different wavelengths of light by photo-receptive cells in the body. No light, no observing body, nothing is classed as being a "Colour". That also has a little to do with Quantum Physics as well. go look of the Double slit experiment and how it pertains to the old Schrödinger's Cat paradox.

I guess i would have to retract the comment about there being no light inside the body. Light does penetrate the outer surface of our body, and the Body also produces light in a process known as Bio-Photonics or Bio-Electromagnetism. However, although the "Colour" of the compound could play more complex, atomic roles in the body, there is still no conscious observer, meaning there is not really a "Colour".

@ Doria. I'm sorry, but half the garbage you are fed in grade school is just that. Garbage. I completely broke away from the public educational system in the 10th grade, because i was being taught simpleton crap like what you are talking about right now. Chemically, blood bound to carbon dioxide is blue, end of story. I've had "Biology" teachers tell me carbon is toxic, complete combustion isn't dependant on oxygen presence, that radiation at any dose is harmful, and that BT Toxin is completely safe. Wake up, for your own sake.

All these brainwashed morons repeating BS they read instead of looking into it, weather its "Peer reviewed" (which means nothing in the real world of science) or not, just goes to show you how dead real science really is. Moronic comments like "Not naturally possible", "Never" and, "I've dissected animals and haven't seen it" hold no scientific foundation. Clearly, none of you understand what "Blood" even is, or how "Colour" even works.

Jason, you obviously think you know more than anyone else, even the experts! But you still don't know the difference between 'whether' and weather'. Your choice of words also reflects your level of education. And please don't blame your teachers and Public School system for your lack of proper education.

I know this sounds extremely hard to believe...if it didn't happen to me personally I would not believe it....believe it or not but I will swear on my mother's grave...when I was about 8years old. I was riding my cousins bike with no shoes. Wasnt going very fast buxt the curbs on the side of the street were the square shaped one's that kind of looklike a step. My toe scraped the curb and got jammed between the curb and my cousins bike pedal. My toe was gushing out blue blood the entire time. Blue blue....not people, not dark red , not red, was blue like smurf blue...all my cousins seen it , my brother and sister remember was very scary as a little boy.knowing that blood was suppose to be red I thought something was wrong with me

By Shawn Anderson (not verified) on 02 Mar 2014 #permalink

I see blood all day long because I am a dialysis nurse. When you have a patient with a central venous catheter, you access blood flow in the superior vena cava. This is a vein right above the entrance to the heart. The blood is darker red than arterial blood, which we access when the patient has an arterio-venous fistula. It never hits oxygen because it is taken out of the body, cleaned, and returned in a sterile closed system. Blood is always red or darker red.

By Elizabeth (not verified) on 03 Jun 2014 #permalink

All I want to no is every body's blood is red as soon they show blue blood on the news then I will be leave this other than that everybody's blood is red

When I was 10, I jammed my left big toe and cut it across the top of it on my bedframe. I freaked because it was dripping dark blue blood (and hurt!!!)... I ran to show my mom, telling her I was bleeding BLUE, and she said I was being overly dramatic (as I could be) until she saw it. And then she got into "mom" mode and worked to help me bandage it. She explained to me it was because something had happened that made it so the type of cut I had was one in which the blood hadn't been oxygenated yet. Took me awhile to wrap my head around, but after a few more years in school and studying A&P, what she said and what's explained here makes sense.

I have been asked questions by kids, of various ages, whether blood is bue, because their teachers told them it is. I even had an argument with my neice, where she took her teacher's word over mine, when she asked if human blood is blue, and I told her, "no, it is not." I am a med tech that has worked in a lab setting 17 yrs and have had my share of blood samples and specimens, and I have yet to ever see "blue" blood. I have seen dark green blood, but it was a sample from a corpse of someone who had OD'd. My neice said that her teacher taught the class that blood was the color of the picture in the textbook, not magenta, not dark purple, but prussian type blue. She said that unoxygenated blood is blue. My argument was that when the blood flows from the vein where deoxygenated blood is, into the tube, you can visually see its' color, which is deep red, almost brown to purple, but definitely not blue. She refused to believe me. This was 9th grade teaching at its best, teaching kids to trust their every word. Yet I, the person who works with blood every day, could not convince my own neice that her teacher didn't know everything.

By christina (not verified) on 02 Nov 2015 #permalink

My dads girlfreind is in collage and told me that our blood is blue exiting the heart and whenyou get cut the blue blood is oxygenated it turns red.

By Garmauforever (not verified) on 19 Nov 2015 #permalink

Being exposed to air and oxygenated are being confused. When blood travels through the clear tubing of a heart/lung machine you get a true sense of the color of arterial blood (mixed with oxygen) and venous blood (de-oxygenated). Arterial blood is a bright red and venous blood is a deeper, darker, maroon color. The reason it appears blue under your skin is because the vein walls are a thick milky white color and that acts like a filter making the veins look blue.

I just read an article several months ago that described how the various words in different cultures (in this case color) influences the actual colors we see, which may be the actual reason why some people in the medical profession are saying blood is blue, purple, red, or whatever other color they can think of. Unfortunately, I can't find that article now, but the best explanation is covered here with the examples on blue versus computer blue vs. computer purple and so on. Our language is helping dictate what we are actually seeing.

This is for Jason of Canada (July 20, 2013)
RE, "Light does penetrate the outer surface of our body:"
Light penetrats farther into the body than think. Haven't you ever turned out the lights and put a flashlight on your hand? The red spectrum (red light) goes all the way through your hand.
RE, "...there is still no conscious observer [inside the body], meaning there is not really a “Colour."
1. You have taken too many philosophy classes.
2. Of course there are conscious observers inside the human body. Every pregnant woman has at least one conscious observer inside. Those babies are awash in red glowing light when she gets some direct sunlight on her abdomen.

I have not read every post in this thread so it may have already been commented on regarding the point of veins viewed in the arm having a blue appearance. The light reflecting off of the blood cells in the vein have passed through and been filtered by anatomical structure including the skin. When passes though these mediums, there is some loss and lower frequencies are lost sooner I believe resulting in a blue trend similar to the frequencies lost as you go deeper in water.

There is such thing in blue blood I understand but u can leak blue blood when the blood throw ur wrist it could be not flowing right so u accident cut ur self u bleed blue blood u could be disease or be iron levels but it ur blood there something wrong with it to make u bleed blue blood say ur red blood is flowing but ur blue isn't so u cute ur self and u start to bleed blood and that blue didn't have no else to go and then u could pass out by lose so much blood and I only 15 years old

Good grief. For a start, what the hell does your claim, unsupported by anything, of being 15 years old mean? The only option I see is that you know what you typed is incoherent bollocks and therefore want to have that excused by claiming to be very young.

But that load of verbalvomit was something you only see from four year olds telling their parent breathlessly about what they saw out the car window.

The post was meaningless drivel, and even a 12 year old should be ashamed of such a piss poor attempt at communication.

And 15 year olds don't feel the need to tell everyone out of nowhere that they are 15 years old.

"The reason it appears blue under your skin is because the vein walls are a thick milky white color and that acts like a filter making the veins look blue."

It could be simpler than that. Your visual cognition has no set white balance (see any colour optical illusion image for proof), therefore you rate colours in reference to other nearby shades.

That your darker blood is next to pale pink may cause it to seem less red, which means more blue than it would be if you'd looked at the spectral output of the photons reflected on a plot.

I think blood is blue colour without oxygen