Premenstrual syndrome (PMS) is a condition that affects a woman’s emotions, physical health, and behavior during certain days of the menstrual cycle, generally just before her menses. PMS is a very common condition. Its symptoms affect more than 90 percent of menstruating women. It must impair some aspect of your life for your doctor to diagnose you. PMS symptoms start five to 11 days before menstruation and typically go away once menstruation begins. The cause of PMS is unknown. However, many researchers believe that it’s related to a change in both sex hormone and serotonin levels at the beginning of the menstrual cycle. Levels of estrogen and progesterone increase during certain times of the month. An increase in these hormones can cause mood swings, anxiety, and irritability. Ovarian steroids also modulate activity in parts of your brain associated with premenstrual symptoms.