As noted previously, PMS symptoms appear in the second half of woman’s menstrual cycle, most likely because of the sharp drop progesterone levels. But, as with the length of a normal menstrual cycle, variation is normal.

In the usual scenario, PMS symptoms appear seven to ten days before menstruation and get progressively worse until the day the woman gets her period, at which point they either cease immediately or taper off more gradually (usually within four days of getting a period). A small number of women, between 5 and 10 percent, experience a short burst of PMS symptoms around ovulation. PMS experts believe this may be related to the fall in estrogen that occurs the middle of a woman’s menstrual cycle.

Some women complain of symptoms that begin shortly after and continue throughout their periods. Given that ovulation can occur two weeks before a woman’s period and a period last eight days, this means three full weeks of PMS! In some experts say, this near-constant experience of PMS gets progressively worse and can appear to be a mood disorder.

In another interesting twist, PMS also appears to occur and more severely in women who are thirty or older. women complain that their symptoms get progressively worse age. However, given that PMS can strike a menstruating woman any age—usually starting anywhere from about two years girl starts menstruating, or about age fourteen, all the way to menopause—this increase in severity has some experts One theory is that women forty and older are really experiencing some of the symptoms of menopause or perimenopause but them with PMS. Another is that older women see health-care for non-pregnancy-related reasons more frequently and therefore have more opportunities to seek help for PMS. Finally, a third theory is that the emotional and mood swings so common with PMS are written off in teenagers as part of adolescence. The truth of the matter is that there's not enough information about PMS to tell for certain why older women are more likely to have more severe PMS.