PMS, or premenstrual syndrome, is experienced by an estimated 85 percent of all women at some point during their lives. PMS is an umbrella term used to describe a number of physical and emotional changes that women undergo in the days between ovulation and the onset of the monthly period. These changes are attributed to changing hormone levels in the body.

Increased levels of certain hormones may result in specific PMS symptoms. The secretion of too much prolactin from the pituitary gland causes breast tenderness. Excessive prolactin secretion can also interfere with ovulation and may result in irregular periods. Another hormone, aldosterone, is secreted by the adrenal glands. Aldosterone levels normally increase after ovulation. This hormone acts by causing fluid retention, which in turn leads to bloating, headaches and breast swelling in some women.

The brain does not utilize the mood-stabilizing neurotransmitter serotonin efficiently in some women, resulting in depression or anxiety. Endorphins, which are natural mood enhancers, may be secreted in reduced amounts by the pituitary gland, contributing to depression and to increased pain sensitivity. Increased sensitivity to insulin may result in episodes of low blood sugar, which in turn may increase irritability.

It is not fully understood why some women experience PMS, and others dont. Women with a close blood relative who also has PMS are more likely to suffer from PMS themselves. The types and severity of symptoms vary from one woman to the next. A more severe form of PMS is called premenstrual dysphoric disorder, or PMDD.

In general, PMS tends to become worse the closer a woman gets to menopause. PMS-like symptoms can also be triggered when a woman undergoes major hormonal changes (such as those that occur during pregnancy), when on hormonal contraceptives or after a miscarriage or childbirth.