There are many misconceptions when it comes to the color of blood. Most of them even sound so scientific that we should all be forgiven for being mistaken. Think over some of the things you’ve heard about blood in your life. Like the fact that blood is blue or purple when it’s inside your body or its color comes from iron and hemoglobin. But what’s the truth? What color is blood? Why is it the color it is? How about why it looks different when it’s inside your body than when you’ve grazed your knee?

Is Blood Red?

Yes. Always. Blood is always red. It’s red when it’s inside of your body, coursing through your veins, and it’s red when it comes to the surface, too. There’s even a shade of red named after it, “blood red”! For some reason, a lot of us have heard down the line that blood is actually blue when it’s inside the body. It makes sense; our veins are blue, when you get varicose veins, they look purple. While the shade will change, blood is, undoubtedly, red.

Healthy human red bloodcells abstract concept background


Is Blood Blue?

No, but it’s also very easy to see where this myth came from. You might have heard that the blood inside of us is blue when it's heading back to our lungs because it lacks oxygen. When we lack oxygen, our lips turn blue, so why wouldn't our blood turn blue, too? Although blood looks blue through our skin, the blue is just an optical illusion due to the way the light hits our veins.

blood sample test tube Cecilie_Arcurs / Getty Images


If Blood is Red, Why Are Veins Blue?

Veins actually aren’t blue at all. It’s that tricky optical illusion thing coming into play again. Veins only appear to be blue or purple when they're seen through the skin. When a surgeon cuts a patient open during an operation, they'll see red veins if the blood is pumping and grey if not. Those same veins are the blue veins we see when we look at our wrists or the backs of our hands.

Working wrinkled hands of an old woman


Why is Blood Red?

It would be odd if our blood was yellow. The statements that blood gets is color from hemoglobin are correct. Hemoglobin is an iron that contains protein, carried through the body in our red blood cells. The hemoglobin helps carry oxygen throughout the body, ensuring we get an adequate amount at all times. Our blood actually contains a lot of different things that keep our bodies going. First of all, the most voluminous substance is plasma. Plasma is blood's main component but has an adaptive color that changes according to its surroundings. The red color comes from the hemoglobin and the blood cells, from the protein 'hemes' which binds with iron. Oxygen then bonds with the iron and that interaction is what gives blood its color.

blood donation concept BlackJack3D / Getty Images


Why is Blood Sometimes Dark?

Blood can alternate between shades of red depending on how much oxygen it contains. The more oxygen blood has, the brighter red it appears. On the contrary, the more starved of oxygen blood is, the darker it looks. When you cut yourself, you usually see darker blood. This is venous blood and it has the lowest oxygen levels. There are even times when the blood can be so dark that it looks back. As with veins, the shade tends to depend on the light.

scientist testing blood PeopleImages / Getty Images


What Actually Has Blue Blood?

Although we humans don't have blue blood, there are some organisms on the planet that do. There are also some that have green or even violet blood. But why do they have different colored blood to us? Spiders, crustaceans, and squid all have blue blood. Where we have hemoglobin, they have hemocyanin, which contains copper rather than iron. Some worms and leeches have green blood and their blood contains chlorocruorin. Finally, species with violet or purple blood include some marine worms such as peanut worms and brachiopods.

Men's health check blood pressure


How Much Blood Do We Have?

There's a lot of blood in the human body. An average adult has anywhere between 1.2 to 1.5 gallons of blood, but the volume will vary depending on the person's age or size. Blood also accounts for 7-8% of our total body weight, meaning that if we had no blood, we'd also be 10% lighter. On the other hand, we also wouldn't be alive.

blood testing dish john shepherd / Getty Images


What Are the Blood Types?

Blood type is a classification for our blood. The types are determined by the presence of absence of substances called antigens that trigger immune responses. Blood typing is needed for safe blood transfusions, as there are some blood types that won't mix well with others and some bodies that won't be able to handle different types. There are 8 common blood types: A+, A-, B+, B-, O+, O-, AB+, AB- with the rarest in the United States being AB-negative. O-negative, on the other hand, is known as the "universal blood type" and it's so needed that hospitals across the globe usually have shortages.

scientist in laboratory vitranc / Getty Images


Should I Donate My Blood?

You should donate your blood if you can. You’re losing nothing if you do, and you could potentially be saving somebody else’s life. Blood is precious and a better gift than any scented candle could be. It's a big part of life and a necessary one. Scientists can now split our blood into separated components of red cells, platelets, and plasma, which could save multiple people. There's also evidence that donating blood can improve our cardiovascular and liver health.

blood lab equipment undefined / Getty Images


How Much Blood is it Safe to Lose?

Overall, you can lose up to 40% of your blood and have a chance of survival. Once you lose more than 40% however, it might be more difficult. Adults over the age of 18 can safely donate 1 pint of blood safely, and although you need to wait 56 days between you make donations, you can do it again and again. Roughly 4.5 million Americans need blood transfusions annually with somebody needing blood every two seconds. To donate blood, you'll have to pass certain tests. For example, if you have a specified health condition or are on medication, you might not be able to give blood.

Blood donor squeezes the rubber bulb in the form of heart in his hand


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