Menstruation is a result of puberty. This is when your body becomes capable of reproduction. When your menstrual cycle begins, your estrogen levels increase. That causes the lining of your uterus to thicken. The uterine lining thickens so it can support a fertilized egg and develop into a pregnancy.
If there isn’t a fertilized egg, your body will break the lining down and push it out of your uterus. This results in bleeding — your menstrual period. It doesn’t matter if you’ve had a period for years or you’re waiting for your first one — periods can be difficult to navigate.