Why do human females have periods?

Human females have periods because their bodies are getting ready for a baby every month.

Imagine you have a special box where you keep your favorite toys. Every month, you open the box and take out one toy to play with. If that toy is not used, it goes back into the box, but sometimes it gets pushed out of the box, and you see it on the floor.

That’s kind of like what happens in a female body. Inside, there's a place called the womb, where a baby can grow. Every month, the body makes a special lining that helps hold a baby if one comes. If no baby is there, that lining is pushed out, and that’s what we call a period.

• The body uses hormones like messengers to tell different parts what to do.
• A little egg travels from the ovaries to the womb, where it might meet a sperm (like a friend who helps make a baby).
• If no egg meets a sperm, the lining of the womb is no longer needed, so it comes out.

It’s like cleaning up after playing with your toys, sometimes you have to throw some away, and that's what happens during a period.