As with labels such as “schizophrenia,” and many besides, premenstrual syndrome is a symptomatological diagnosis – a category formed not on the basis of any known cause but on a loosely associated set of symptoms, which are many and vary in severity.
And none of them should exist. Evolution has had a near-eternity to chip away at the reproductive system, and for normal bodily processes to induce pain or debility ought to be selected out unless there is some obvious adaptive trade-off (the only example that comes to mind is giving birth). Furthermore, since these problems are experienced by only a subset of women, they are not an inevitable result of hormone changes.
An alternative explanation is pathogens. During the luteal phase of the menstrual cycle, the immune system is weakened to avoid destroying new embryos, leaving women vulnerable to infectious agents. Empirically confirmed associations of PMS symptoms with pathogens include chlamydia and trichomonas vaginalis, but there could easily be others which have either evaded precise investigation or have been ignored.
The psychic pain brought on by menstruation is well documented. Hippocrates spoke of it, but he was clearly talking about the “madness” that could come as an effect of the physical symptoms such as dysmenorrhoea, not an independent mania or irrationalism brought on by what we now call “being hormonal,” whatever that means.
About one-quarter of women report clinical symptoms of PMS, which are likely to be pathogenic, but a fairly decent percentage of them, with or without the disease symptoms, report other problems such as killing people, screaming Love Island-tier insults at household objects, crying incontinently, losing the ability to turn-take in conversation, psychotic paranoia, and wasting other people’s money.
Lots of physiological processes happen all the time which, theoretically, could have a noticeable impact on mood. Levels of cortisol, the “stress hormone,” shift throughout the day, peaking in the hours just after waking, and drinking alcohol has a far more dramatic impact on nearly all aspects of brain function than anything menstruation does. Yet, the Morning Cortisol Rage has yet to breach the popular lexicon, and the effects of alcohol are closer to being psychosomatic than is ordinarily assumed: it is not a human universal that drinking causes chimpanzee-like states of aggression and disinhibition as it does in Britain. So it looks like another anomaly of our time and place, a thing that exists because people want it to. The same probably holds true for – well, lots of things.
Childhood was a fun time. Maybe it’s not surprising that people love an excuse to return to it; some periodically, others pretty much all the time.