What happens when a girl doesnt bleed on her period?

Menstruation, AKA a period, is when the uterine lining breaks down - if there is no bleeding then she is not experiencing menstruation. A woman can miss her period for a number of reasons, such as stress or ill health, if a woman is in her teens irregular hormones can cause irregular cycles too.

If this is a one off it's nothing to worry about, but if you miss three cycles or more than it's a good idea to talk to your doctor. If sexually active this may also mean pregnancy, so take a test.