Only about 3 to 8 percent of women who report PMS-like symptoms have PMDD; nevertheless, that’s still anywhere from 3 to 5 million women or up to one in twenty women with regular menstrual periods.

PMDD has a biological basis, but it is also affected by psychological, social, and cultural factors, such as being aware of premenstrual syndrome, stress, and socioeconomic status.

If you have a history of depression or postpartum depression, you are more likely to suffer from PMDD. Between 30 and 76 percent of women diagnosed with PMDD have a lifetime history of depression, compared to 15 percent of women of similar age without PMDD. Women with a personal or family history of mood disorders are also at higher risk of developing PMDD.

Other risk factors for PMDD include:

• Experiencing traumatic events, such as rape

• Other existing anxiety disorders, such as seasonal affective disorder

• Premenstrual mood changes

• History of sexual abuse

• Past or present domestic violence

While there is no definitive explanation for PMDD, the most common theory is that PMDD is an abnormal reaction to normal hormonal fluctuations in the central nervous system. The abnormal reaction affects brain chemistry, especially serotonin. For example, research shows that women with PMDD have reduced serotogenic activity. The cyclical nature of PMDD also suggests that the sex hormones estrogen and progesterone alter the levels of neurotransmitters, including serotonin. In addition, the success of selective serotonin reuptake inhibitors (SSRIs) such as Sarafem or Sertraline in treating PMDD symptoms makes a strong case for the importance of serotonin in PMDD.

Finally, there is some evidence there may be a genetic component to PMDD and PMS. Women whose mothers had PMS are nearly twice as likely to have PMS themselves— 70 percent compared to 37 percent of women with PMS whose mothers did not have PMS. Identical twins are more than twice as likely to have PMDD than fraternal twins; 93 percent of identical twins share PMDD, while only 44 percent of fraternal twins do.

Theories on the Causes of PMDD

There are several major theories used to explain the causes of PMDD:

• Ovarian hormone theory: PMDD is caused by an imbalance in the ratio of estrogen to progesterone, especially a relative deficiency in progesterone. Studies on this theory have been inconclusive.

• Serotonin theory:Normal hormonal fluctuations cause changes in a woman's brain chemistry, particularly in the serotonin system, causing PMDD symptoms. This is currently the leading theory.

• Psychosocial theory:PMS and PMDD are conscious of a woman’s unconscious conflicts about her society.

• Cognitive–social learning theory: Many women are psychologically averse to their periods and have negative or extreme thoughts that reinforce their aversion to premenstrual symptoms. In response, they develop inappropriate coping strategies, such as mood swings or overeating, which reduce their stress temporarily but also set them up to repeat the process month after month.