Why is blood red? — Simple explanation for a 6-year-old

Why is blood red?

You are right that blood has many red cells. Those tiny things are called red blood cells. They are like little boats that carry something very important called oxygen to every part of your body.

1. Red blood cells are most of the cells in blood. They are the things that make blood look red.
2. Inside each red blood cell is a helper called hemoglobin. Hemoglobin has iron inside it — Iron is a little bit like the rust on a bicycle which is reddish. That is why hemoglobin looks red.
3. When hemoglobin carries oxygen, it looks bright red. This is the blood that comes from your heart to all your body parts.
4. When the blood has less oxygen (after it brings oxygen to the body), it looks a darker red. Even though veins sometimes look blue through the skin, the blood inside them is dark red, not blue.

Simple way to see the idea

Try a drawing: color one circle bright red for oxygen-rich blood and another circle dark red for oxygen-poor blood. That shows how the color can change a little.

Remember: Blood is red because of the red blood cells and the hemoglobin (with iron) inside them. The color changes from bright red to darker red depending on how much oxygen it is carrying.

If you want, draw a picture of red blood cells carrying tiny oxygen bubbles — it can be a fun way to remember!