Red blood cells

Red blood cells are tiny red disks that carry oxygen from your lungs to every part of you.

Red cells, white cells and tiny platelets ride along in yellowish plasma. Tap any part!

Donuts without a hole

A red blood cell is a round, flat disk that is pushed in on both sides. It looks like a donut that forgot to get its hole.

That shape gives it lots of outside surface, so oxygen can get in and out fast.

Red blood cells are bendy, too. They can fold and squeeze through capillaries that are even narrower than they are, then pop back into shape.

They are tiny. About 10 of them lined up side by side would be about as wide as one hair.

Oxygen carriers

Each red blood cell is packed with hemoglobin (HEE-muh-glow-bin). Hemoglobin is like a set of tiny hands that grab on to oxygen.

In the lungs, the hands grab oxygen. Out in the body, where cells need it, they let go.

Hemoglobin is what makes blood red. It uses iron to hold on to oxygen. That is why eating foods with iron helps your blood.

So many of them

Red blood cells are by far the most common cells in your blood. A tiny speck of blood about as big as a pinhead holds about 5 million of them. A whole drop holds hundreds of millions.

A grown-up has about 25 trillion red blood cells. That is 25 with twelve zeros after it!

If you counted every cell in your body, more than 8 out of 10 would be red blood cells.

No middle

Most cells have a nucleus (NOO-klee-us), a center that holds the cell's instructions. Grown-up red blood cells do not! They push it out before they leave the bone marrow.

That leaves more room for hemoglobin, so each cell can carry more oxygen.

Without a nucleus, a red blood cell cannot fix itself or make new parts. So after a while, it wears out.

Born in your bones

Red blood cells are made in bone marrow, the soft, spongy middle of some of your bones, like your hips, ribs and backbone.

Your bone marrow makes millions of new red blood cells every second, all day and all night.

A red blood cell lives for about 120 days, about four months. In that time it zooms around your body many thousands of times.

Old red blood cells are taken apart in your spleen and liver. Your body even saves their iron to build new ones.

🤩 Wow facts

More than 8 out of 10 cells in your body are red blood cells.
A grown-up has about 25 trillion red blood cells.
Each red blood cell lives about 120 days, then gets recycled.
Red blood cells have no nucleus, the center that most cells have.
Each red blood cell is packed with hundreds of millions of hemoglobin bits, and each bit can carry four tiny pieces of oxygen.
Your body saves the iron from old red blood cells to build new ones.
People who live high up in the mountains often have more red blood cells, to catch more oxygen from the thin air.

💚 Look after it

Eat foods with iron, like beans, lentils, spinach, eggs, meat and iron-fortified cereal.
Have fruits like oranges or strawberries with those foods. Their vitamin C helps your body take in iron.
Drink water every day.
Play outside and get moving.

🩹 When something goes wrong

Feeling very tired. When a body does not have enough red blood cells or iron, a person can feel tired or weak, or look pale. This is called anemia (uh-NEE-mee-uh), and doctors know how to help. If you feel tired a lot, tell a grown-up so they can check with a doctor.

🙋 Questions kids ask

Why are red blood cells shaped like that?

The pushed-in shape gives them lots of surface to grab oxygen, and lets them bend to squeeze through tiny tubes.

What happens to old red blood cells?

After about four months, your spleen and liver take them apart. Your body saves the iron to build new ones.

Why do I need iron?

Iron is part of hemoglobin, the stuff that holds oxygen. Without enough iron, your body cannot make enough healthy red blood cells.

🧠 Quick quiz

Question 1 of 3What does hemoglobin carry?

🔊 Donuts without a hole

🔊 Oxygen carriers

🔊 So many of them

🔊 No middle

🔊 Born in your bones