Menstruation — aka having your period — is when blood and tissue from your uterus comes out of your vagina. It usually happens every month.

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.

What created periods?

Your cycle uses hormonal signals as cues for what to do next. In the first part of your cycle, one of your ovaries prepares to release an egg. It also produces an increasing amount of the hormone estrogen. This estrogen helps grow and prepare the lining of your uterus (the endometrium) for a potential pregnancy (1).