Yes, especially if you are thin or not taking in enough nutrition to fuel your body. Participation in gym class exercise or an afterschool soccer team usually doesn’t affect your periods. However, if you are very active and train hard (play an intense sport or exercise for hours at the gym), your period may be lighter. Some girls may begin to skip periods if they are not getting enough nutrition, have an eating disorder, are stressed, or are over-exercising. It’s a good idea to keep track of your menstrual cycle so you can tell your health care provider when your period/cycles change. If you are sexually active and notice your period is lighter than usual, it could mean that you are pregnant. Either way, talk to your health care provider if your period changes.