A period happens because of changes in hormones in the body. Hormones give messages to the body. These hormones cause the lining of the uterus (or womb) to build up. This gets the uterus ready for an egg (from the mom) and sperm (from the dad) to attach and grow into a baby.

What do guys have instead of periods?

Of course, men don't actually have the lovely bonafide PMS related to preparing the uterus and egg for fertilization. But some go through what's called the male PMS: "IMS" (Irritable Male Syndrome). This can be attributed to men experiencing a drop in testosterone, the hormone that gives them their mojo.

Why is my period blood bright red?

‌Bright red blood: As your uterus starts to actively shed blood during your period, you may notice that the color is bright red. This just means that your blood is fresh and has not been in the uterus or vagina for some time.