Medically reviewed by Cordelia Nwankwo, MD Key Takeaways Breast development usually starts about two years before the first period. Emotional changes and mood swings can occur just before the period.

Around half of teenage girls experience moderate to severe period pain. The mechanical force of the uterus contracting and inflammatory chemicals such as prostaglandins contribute to this pain.

For decades, most girls experienced their first menstrual period between the ages of 11 and 13. Today, however, doctors are seeing a noticeable shift. An increasing number of girls are entering ...