A quick glance at the wrist and it's easy to understand why people may think their blood is blue. After all, the veins look blue. But is blood blue? The answer is no.

In this article, we look at a variety of facts about blood, including color, types, and donation.

Is blood blue? Debunking a popular myth. Share on Pinterest
It is a myth that deoxygenated blood is blue; all blood in the human body is red.

Human blood contains hemoglobin, which is a complex protein molecule in red blood cells.

Hemoglobin contains iron. The iron reacts with oxygen, giving blood its red color.

Although veins appear blue through the skin, blood is not blue. The reason why veins might seem to be blue may have to do with the level of oxygen in the blood.

Arteries transport blood that is rich in oxygen away from the heart to be used by organs and tissues in the body. The veins return deoxygenated blood to the heart.

It is a common myth that veins are blue because they carry deoxygenated blood. Blood in the human body is red regardless of how oxygen-rich it is, but the shade of red may vary.

The level or amount of oxygen in the blood determines the hue of red. As blood leaves the heart and is oxygen-rich, it is bright red.

When the blood returns to the heart, it has less oxygen. It is still red but will be darker. This darker red appears blue because of how light travels through the skin.

Similar to people, most animals also have red blood. However, there are a few exceptions.

Some types of octopus, squid, and crustaceans have blue blood. Their blood contains a high concentration of copper. When copper mixes with oxygen, it gives their blood its blue color.

Blue and red are not the only possible colors of blood — some animals bleed green.

The skink, which is a type of lizard, has green blood due to a buildup of biliverdin. Biliverdin and bilirubin are by-products of the liver. Humans also produce these two by-products.

However, the human body sends biliverdin and bilirubin to the intestines and through the digestive system to be excreted. Skinks do not excrete biliverdin, so it builds up in their body, making the blood green.

Everyone knows that blood is a vital component of the human body. But just how much blood is in the body? The exact amount of blood in the body varies according to a person's size. The larger a person is, the more blood volume they have.

Approximately 7–8 percent of a person's total weight is blood. That means an average-sized woman has about 9 pints of blood and an average-sized man about 12 pints.

If a person loses too much blood, it can lead to a life-threatening condition called hemorrhagic shock.

Research shows that shock usually occurs when a person loses 20 percent of their blood volume.

Symptoms of hemorrhagic shock include dizziness, low blood pressure, and confusion. A doctor will likely treat hemorrhagic shock with fluid resuscitation and blood transfusions.

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Although everyone's blood contains the same elements, not everyone's blood is the same.

Everyone's blood contains the same elements or components. Human blood contains red cells, white cells, platelets, and plasma. Even though all blood contains those same components, not everyone's blood is alike.

There are different blood types based on the absence or presence of specific antigens and antibodies on the surface of the red blood cells. An antigen is a substance that can cause an immune system response in the body.

The two most common antigens are A and B. For example, people with the blood type A have an A-antigen on their red blood cells, and people with type B blood have a B-antigen. Some people have both.

People with O blood type do not have either A or B antigens on the red blood cells. Type O is the most common blood type in the world.

Another antigen is a protein called the Rhesus (Rh) factor. People with this protein are considered Rh-positive. If the blood lacks the protein, they are Rh-negative.

It is more common to have Rh-positive blood than Rh-negative. If a person who is Rh-negative needs a transfusion, they should not receive Rh-positive blood.

Anyone of any ethnic group can have any blood type, but there are some ethnic and racial trends.

For example, having blood type B is relatively common for people who are Asian or of Asian descent.

Although A and B are the most common antigens, there are many other less common antigens that create rare blood types.

Certain rare blood types are unique to specific racial and ethnic groups. For example, blood type RzRz is unique to Native Americans and Alaskan Natives.

Blood transfusions are when healthy blood from a donor is injected into a person who needs it.

Common reasons to have a blood transfusion include:

  • Severe blood loss from surgery, an accident, or childbirth.
  • Anemia, when a person does not have enough red blood cells.
  • Some types of cancer and cancer treatment, including chemotherapy.
  • Conditions that affect the red blood cells, such as sickle cell disease.

If a person requires a blood transfusion, it is essential that the blood type they are given is a compatible type. If a person receives an incompatible blood type, their immune system may reject it. This can be life-threatening.

Most people can receive type O blood safely, regardless of their blood type. This is why most blood donation clinics are in need of type O blood, as it can be used to help many people.

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Donating blood can save lives, with estimates suggesting someone needs blood almost every 2 seconds worldwide.

Without a blood transfusion, significant blood loss or severe anemia can be life-threatening.

Donating blood can save lives. For those who are unsure about donating blood, it is helpful to consider the facts below:

  • Around 5 million people in the United States receive blood each year.
  • The Red Cross estimates that someone needs blood about every 2 seconds.
  • Although research is underway to make synthetic blood, currently blood for transfusions only comes from donors.
  • Typically, a person will donate just 1 pint of blood at a time.
  • Most people do not develop side effects from donating blood.

Blood is essential for the functioning of the human body, but many myths about the body persist. Having accurate information about blood or any other aspect of health is vital.

If someone is in doubt about a health issue, it is essential to talk to a doctor to get the most accurate information.