Human blood is red – this is an axiom, that is, a statement that does not require any evidence. You may have heard the expression “blue blood”, which means that a person belongs to the upper strata of society. However, the fluid flowing through our veins cannot be colored this color – this only happens in specific cases. But the blood may well take on a greenish tint. This occurs either at great depths in the seas and oceans, or under certain environmental conditions on land. For many people, this can be a big discovery that requires detailed explanation. Right now we will tell you everything in detail – read and expand your horizons!
Underwater, human blood turns green, and there is a scientific explanation for this
What happens to a person under water
If a person dives into the sea or ocean to a depth of more than 20 meters, and then a wound appears on his body, green blood will flow from it. Once this happened to a scuba diver – when he was at the bottom of the sea, he was bitten by a toothy moray eel fish. The photo below shows green blood oozing from their wound on his finger.
Green blood comes from a scuba diver's wound. Image: YouTube channel of user Tim Powell
Morayis a long fish that has no fins and resembles a snake in its appearance. She lives in the depths of seas and oceans, hiding in rocky shelters. They have sharp teeth that have long been considered poisonous. But there is no poison in them, although moray eel bites are very painful.
Moray eel fish. Image: flomaster.top
You might think that something wrong happens to the human body in water, and his blood changes its composition. Of course, at great depths a person is under great pressure, and at a minimum he experiences breathing problems even with scuba gear. But the reason for the greenish tint of blood is different – the composition does not change, we just begin to see it through a water filter.
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Why is blood green underwater
We all know from school that we see different colors due to the fact that light is reflected from objects and enters our eyes. Each color has its own unique wavelength: for example, red has longer waves than blue or green.
When we are on the surface of the earth, all the colors around us are perceived naturally by us. Blood appears red, grass appears green, sky appears blue, and so on. However, when we dive deeper underwater, the water begins to absorb some light waves. Red waves are blocked first, while green and blue waves pass through the water better.
In the depths of the oceans it is impossible to see the color red. Image: dailymail.co.uk
Therefore, when we see blood at great depths, it may appear green rather than red. This effect is explained by the fact that water acts as a filter, leaving only some colors visible at depth. This effect may explain why many deep-sea creatures are colored red. When they are at great depths, they become very dark, making them often undetectable by predators. For example, it is for this reason that evolution has endowed deep-sea crayfish with a red body.
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Because of- why does blood change color
In rare cases, human blood actually turns red, and this is not an optical illusion.
Human blood is red due to the content of hemoglobin – a protein that carries oxygen from the lungs to all other organs. It contains many iron ions, which turn red when in contact with oxygen from the lungs.
In rare cases, blood can actually turn green
Human blood can turn green if hemoglobin binds to sulfur atoms. They prevent iron from binding to oxygen, so the blood appears greenish and sometimes even black. This usually occurs due to the use of certain medications, as well as after exposure to sulfur while working in certain workplaces. This phenomenon is called sulfhemoglobinemia and usually does not require treatment – over time, the natural color of the blood is restored.
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At the beginning of the article it was mentioned that in very rare cases, human blood can turn blue. In 2019, this happened to a young girl – she came to the hospital complaining of weakness, breathing problems and a bluish tint to her skin. While taking tests, doctors were surprised that her blood was colored deep blue. You can read about why this happened in our article “What causes human blood to turn blue.”