Written by Sophia

Modified & Updated: 16 May 2024

Jessica Corbett

Reviewed by Jessica Corbett

They say blood is thicker than water. Maybe it’s not always true, but these blood facts will surely make you marvel at the amazing fluid running through your body this very moment.

  1. Blood is a bodily fluid that transports nutrients and oxygen.
  2. It carries metabolic wastes (such as carbon dioxide) out of the system.
  3. For vertebrates, it is made of 45% blood cells and 55% blood plasma.
  4. Hemoglobin makes human and some animal blood red.
  5. There are 30 recognized blood types in humans.
  1. Blood makes 7% of a human’s weight.
  2. Red blood cells carry oxygen through the body.
  3. White blood cells defend the immune system against diseases, viruses, and other harmful elements.
  4. Platelets prevent blood loss through clotting.
  5. Stroke and heart attacks usually occur due to clots in the brain. 
  6. Blood pressure is usually taken from the upper arm.
  7. Blood pressure refers to the pressure of blood flow on the blood vessels.
  8. Nosebleeds happen because of broken blood vessels.
  9. The usual blood loss during menstruation is 10 to 35 ml. 
  10. Menstruation may cause iron levels to drop.


  1. 3 to 4% of people suffer from blood injury injection phobia (BII). This fear of blood may lead to fainting in severe cases.   
  2. Scientists can’t explain why people have different blood types.
  3. People used to think the lungs transported blood through the body.
  4. Hematophagy refers to the consumption of blood. 
  5. Around 300 to 400 insect species are vampiric. Some birds, mammals, and fish also consume blood.
Table of Contents

Blood Facts Infographics

Blood Facts Infographics

Blood is a delicacy in some cultures.

black pudding blood facts
Source: Pixabay

Black pudding is a blood sausage originating from England and Ireland. Most of their savory dishes feature blood as a base. Some Asian countries also use animal blood for different types of stew, pudding, and other dishes. However, some cultures see the consumption of blood as a taboo. 

People drink blood, too.

The Maasai people of Africa mix cow’s blood with cow’s milk as a staple food. They are a herder culture that places high regard for their cows. As such, they don’t kill their livestock. Instead, they nick the jugulars to get blood without killing them.

You have more than a gallon of blood in your body.

The typical adult has about 1.325 gallons of blood. If you lose 40% of your blood, it could be fatal. You could die if you don’t immediately get a transfusion or medical attention. Pregnant women have 30-50% more blood volume than women who are not pregnant. 

You're made of gold.

A person weighing 70 kg has 0.2 milligrams of gold in their blood (along with iron, chromium, manganese, zinc, lead, and copper). Our bodies have trace amounts of this precious metal.

Insects and invertebrates have blood. 

insect blood facts
Source: Pixabay

Next time you squish a bug, take a closer look. Hemolymph is barely noticeable because it doesn’t have the hemoglobin that makes ours red. Instead, it has a pale and/or yellowish color. 

Some animals have blue blood.

No, they aren’t royalty. But one of the neatest blood facts is that some crustaceans (our crab friends), spiders, octopuses, and squids are blue-blooded because of the protein hemocyanin. Instead of iron, their blood contains more copper.

Some animals bleed green. 

The chlorocruorin blood protein in segmented worms, leeches, and some marine worms makes their blood green. 

Some animals have purple blood.

Perhaps one of the more fabulous blood facts: some creatures bleed purple due to haemerythrin. This is mostly observed in marine worms and brachiopods (mollusks that fold laterally).

You have more in common with earthworms than you think.

Source: Pixabay

Unlike other invertebrates, earthworms bleed red since their blood contains hemoglobin. 

Older people are more prone to stroke because of capillaries.

Capillaries are blood vessels that serve various functions in our organs. In the brain, they filter out cholesterol, calcium plaque, and blood clots. Capillaries recede with age, it this could be a factor in older peoples’ tendency for stroke.

Scientists didn't figure out the circulatory system until the 17th century.

William Harvey discovered that blood is pumped through the heart, not the lungs. This is also the guy that was sent by King James I to investigate a woman accused of witchcraft. How did he do it? He dissected the poor woman’s pet toad to see if there was anything supernatural to it. 

Blood might be used to treat Alzheimer’s.

Scientists injected old mice with blood plasma from younger mice and found that it improved the older mice’s memory and learning. Additionally, it restored the older mice’s organs. Whether this will work with humans is unknown.

Dogs have more than a dozen blood types. 

It’s not just humans that have blood types. However, we have more variations in types.

People thought a tuberculosis epidemic was vampirism.

vampire blood facts
Source: Pixabay

One of the weirder blood facts, a tuberculosis epidemic in 19th-century England had the townspeople thinking something supernatural was going on. It doesn’t help that the outbreak occurred at the peak of vampire claims.

Brain freeze is caused by our blood.

brain freeze blood facts
Source: Pixabay

The notorious ice cream headache is a result of the quick dilation of the brain’s anterior cerebral artery. Sudden temperature changes in the mouth trigger this response which gives us the jarring headache.

O+ is the most common blood type.

The O+ blood type is the most common, comprising 37.4% of the U.S. population. People with O blood are “universal donors” because their blood doesn’t have antigens. Their blood type is compatible with any receiver. However, they can only receive blood from fellow O blood types.

AB- is the rarest blood type.

The AB- blood type is the rarest, making up only 0.6% of the U.S. population. The AB blood type is the “universal receiver” since it has both A and B antigens. Other blood types are usually compatible with them.

The Rhesus factor determines blood types.

blood type blood facts
Source: Pixabay

The Rhesus (Rh) factor is a protein in blood that affects compatibility. Most people have Rh+ blood. Rh- blood types can only receive blood from fellow Rh negative donors. Rh+ blood types can receive from both Rh+ and Rh- donors. Transfusion of incompatible blood types can be fatal, since opposite antigens will destroy each other. This could make life-threatening situations even worse. Thankfully, the medical process of donating and transfusing blood is stricter and more thorough now.

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