The exact cause of premenstrual syndrome (PMS) is not known. However, several factors have been identified as possible causes or contributors to its occurrence. They include:

• Hormonal changes. During the second half of the menstrual cycle (the last 14 days of a 28-day cycle), levels of the hormones estrogen and progesterone increase until approximately day 21 and then begin to fall. Tissues throughout the body are sensitive to these changes.
  
  
• Chemical changes. Fluctuations in levels of serotonin, a brain chemical linked to mood states, may be a cause. Insufficient serotonin levels have been linked to depression, and excess levels have been linked to anxiety.
  
  
• Diet. Some PMS symptoms have been linked to deficiencies in calcium and vitamins A, E and B (which helps to produce serotonin). Certain foods and beverages have also been identified as possible contributors to PMS, including:
  
  
• Sodium. Eating salty foods in excess may cause fluid retention and bloating.
  
  
• Alcohol or caffeine. Drinking beverages containing alcohol or caffeine may cause changes in mood or energy level.

Occasionally, some women with severe PMS have undiagnosed depression, though depression alone does not cause all of the symptoms associated with PMS. Stress may aggravate some of the symptoms, but is not a cause of PMS.

A number of factors may put a woman at higher risk for PMS. They include:

• Depression. Women with a history of depression or postpartum depression have a higher incidence of PMS.
  
  
• Heredity. Women with a family history of PMS are more likely to have PMS.
  
  
• Children. Women with more children are more likely to experience more severe symptoms than women with fewer children.
  
  
• Physical activity. Sedentary women are at a higher risk for PMS than those who exercise regularly.