What causes PMS?

PMS is caused by the normal hormonal cycle, not by anything going wrong in your body. Estrogen rises through the first half of your cycle and peaks just before ovulation.

After ovulation, both estrogen and progesterone rise again during the luteal phase, then fall sharply in the final week or two before your period starts. That drop changes levels of serotonin and other brain chemicals that affect mood, sleep and appetite.

Researchers have looked for one clear cause since the 1950s, testing everything from hormone levels to vitamin deficiencies to psychological factors. A long-running review of this research concluded that no single organic or psychological explanation fits PMS on its own (Canadian Journal of Psychiatry, 1985) [1]. Most scientists now describe PMS as the result of several factors interacting, not one trigger.

That means there's no blood test that confirms PMS. The diagnosis rests on tracking your symptoms against your cycle, which also helps you figure out when your PMS tends to start.

Estrogen and progesterone are the two hormones most closely tied to PMS, though neither one causes it by acting alone. Both rise after ovulation and fall sharply in the final week of your cycle, and that fall is the trigger most researchers point to.

One evolutionary explanation suggests these hormones also shift your immune system, cyclically raising and lowering immune suppression, which this review proposes may help explain why some chronic illnesses of uncertain cause flare in the same window (Perspectives in Biology and Medicine, 2007) [2].

The drop in hormone levels, not a high or low level on its own, seems to matter most. Your body follows roughly the same hormone pattern whether or not you get PMS.

What differs is how sensitive your brain is to that pattern, which is part of why PMS can look so different from person to person. Understanding the luteal phase helps explain why the timing is so consistent even when symptoms aren't.

PMS severity varies widely, and part of that is simply how common it is reported to be.

Numbers this far apart mostly reflect differences in how studies define and measure PMS.

A few things seem to explain why severity differs between people:

• Genetic differences in how sensitive your brain is to normal hormone swings
• Baseline anxiety or mood sensitivity before the hormone drop even starts
• Added physical stress, like poor sleep or inflammation, stacking on top of the hormonal shift

Studies comparing women with PMS to women without it have found higher markers of inflammation and lower antioxidant levels in the PMS group, though the evidence isn't strong enough yet to say inflammation causes the condition (Antioxidants, 2021) [8]. If your PMS feels severe enough to disrupt your week most months, see how much it's affecting you.

Diet and stress don't cause PMS on their own. The hormonal shift happens whether your week was calm or chaotic, and whether you ate well or skipped meals. But both can turn up the volume on symptoms you already have.

The evidence so far:

• Exercise: a review that included 15 trials pooled data from seven of them and found regular exercise reduced overall PMS symptoms compared with no exercise, though results varied a lot between studies (BJGP Open, 2020) [4].
• Vitex agnus-castus (chasteberry): several small trials found it eased symptoms more than placebo, though trial quality varied and sample sizes were small (American Journal of Obstetrics and Gynecology, 2017; Archives of Women's Mental Health, 2017) [5] [7].

Managing stress and building in regular movement can ease the week before your period, even while the hormone shift keeps happening underneath it.

You can't stop estrogen and progesterone from falling before your period. That part of the cycle isn't optional. What you can change is how hard the drop lands and how early you catch the pattern.

A few steps with real evidence behind them:

1. Track your cycle for two to three months with a PMS calculator so you know roughly which days are hardest.
2. Build in regular exercise most weeks; trials show it eases overall PMS symptoms over time [4].
3. Ask a doctor or pharmacist about chasteberry if you want to try a supplement with some trial support, though quality varies [5] [7].
4. Plan lighter weeks and more rest for the days you expect to be hardest.

If you want somewhere to put a hard moment before you react to it, Niyora is a PMS and PMDD support app. Its Moon tool lets you write down what happened, see it from another angle, and draft a reply you can hold onto for 20 minutes before you send anything.

PMS research keeps evolving, but the pattern that matters most is the one in your own cycle. If you want the fuller picture, what PMS is and how it differs from PMDD breaks it down further.