Most people with premenstrual syndrome experience only a few of the possible symptoms, in a relatively predictable pattern.Premenstrual dysphoric disorder (PMDD) is a severe form of premenstrual syndrome affecting 3–8% of menstruating women. Causes
While PMS is linked to the luteal phase, the causes of PMS are not clear, but several factors may be involved. Changes in hormones during the menstrual cycle seem to be an important factor, with changing hormone levels affecting some more than others. PMS occurs more often in those who are in their late 20s and early 40s, have at least one child, have a family history of depression, and have a past medical history of either postpartum depression or a mood disorder. Diagnosis
There are no laboratory tests or unique physical findings to verify the diagnosis of PMS. The three key features are:

The chief complaint is one or more of the emotional symptoms associated with PMS. Irritability, tension, or unhappiness are typical emotional symptoms. Symptoms appear predictably during the luteal (premenstrual) phase, reduce or disappear predictably shortly before or during menstruation, and remain absent during the follicular (preovulatory) phase. The symptoms must be severe enough to interfere with the person’s everyday life.Mild PMS is common, and more severe symptoms would qualify as PMDD. PMS is not listed in the DSM-IV, unlike PMDD. To document a pattern and determine if it is PMDD, potentially affected women may keep a prospective record of their symptoms on a calendar for at least two menstrual cycles.
The variant Val92Met arose somewhere between 250,000 and 100,000 years ago, long enough for this gene to be carried by humans into central Asia. Arg160Trp is estimated to have arisen around 80,000 years ago while Arg151Cys and Asp294His have been estimated to arise around 30,000 years ago. The wide variation of the MC1R gene exists in people of European descent because of the lack of strong environmental pressures on the gene. The original allele of MC1R is coded for dark skin with a high melanin content in the cells. The high melanin content is protective in areas of high UV light exposure. The need was less as humans moved into higher latitudes where incoming sunlight has lower UV light content. The adaptation of lighter skin is needed so that individuals in higher latitudes can still absorb enough UV for the production of vitamin D.  Freckled individuals tend to tan less and have very light skin, an adaptation to allow individuals that expressed these genes to synthesise sufficient vitamin D.

Types
Ephelides describes a freckle that is flat and light brown or red and fades with a reduction of sun exposure. Ephelides are more common in those with light complexions, although they are found on people with a variety of skin tones. The regular use of sunblock can inhibit their development. Liver spots (also known as sunspots and lentigines) look like large freckles, but they form after years of exposure to the sun. Liver spots are more common in older people.