Something I have been sitting with for a while is the particular texture of a week in which everything is harder, not harder because anything has changed, but harder in a way that feels sourceless. A difficult conversation that would normally roll off lodges somewhere behind the sternum. A request that would usually be fine arrives as an imposition. The gap between what happens and how it lands seems to have widened, with no obvious explanation.

Most of the women MoMo works with have a version of this. Many have quietly charted it over time, noting the correlation, then doubting it, then noticing it again. The doubt tends to win, because the cultural vocabulary for what they are experiencing is still mostly made of the wrong words: "hormonal," wielded as an insult; "PMS," a punchline rather than a description. The research has been catching up, and it offers something more precise: the pattern has a name, and the name changes what it means.

Sensitivity, not instability

The scientific framing I keep returning to is affective sensitivity to endogenous ovarian hormones, a measurable, quantifiable individual trait documented in a 2024 study in Psychoneuroendocrinology.[1] The researchers used time-lagged cross-correlations between hormone assays and daily mood data to show that the degree to which a person's emotional state tracks with their hormonal fluctuations is not a subjective impression. It is something that can be measured. It varies between individuals. And crucially, it is framed (explicitly, in the paper) as a sensitivity, not as a pathology.

This matters because of what it is not. It is not mood instability. A 2025 theoretical framework in Molecular Psychiatry proposes three distinct dimensions of hormonal-affective sensitivity across the cycle, and distinguishes these explicitly from mood dysregulation as a trait.[3] The framing is that the same biological fluctuations produce different emotional responses in different people (some experience minimal change, others pronounced) and that this variation is real and documented, not imagined or exaggerated.

If you have ever been told you are "too emotional" at a particular point in the month, that framing gives you something accurate to hold instead.

The window, not the person

A 2026 longitudinal study followed 68 naturally cycling women across 75 days and tracked daily fluctuations in stress vulnerability alongside mental health outcomes.[4] What the researchers found was that stress vulnerability (the ease with which a person tips toward distress when pressure arrives) increased during the peri-menstrual phase. Importantly, this increase preceded changes in anxiety and mood symptoms, rather than following them. In that study at least, the sensitivity window opened first. The difficulty followed.

What that means, translated away from the research language: the days before a period are not days in which the person is different. They are days in which the same person is passing events through a differently calibrated system. The events are the same weight. The system is weighing them differently.

A 2025 study in Psychology of Addictive Behaviors adds a layer.[2] It found that pre-existing difficulties with emotion regulation amplify perimenstrual distress. The cycle effect is not uniform but is larger in people who already find emotional regulation effortful under ordinary conditions. This is consistent with a sensitivity-meets-context model: the cycle does not generate the difficulty from nowhere, but it widens the aperture through which difficulty is experienced.

Not a unified thing

One of the most useful things in the Molecular Psychiatry framework is that it refuses the neat four-phase model that dominates wellness content.[3] That model (follicular is good, luteal is hard, ovulation is peak) is a simplification the evidence does not support. The framework proposes instead that hormonal-affective sensitivity operates on at least three dimensions: negative affect associated with the luteal phase, negative affect specifically associated with the peri-menstrual phase (linked primarily to estradiol decline, though the mechanistic literature remains contested[6]), and a third dimension involving dysregulation of positive affect around ovulation in some individuals.

The practical upshot: there is no universal hormonal mood arc. The pattern is individual-specific. Some women show minimal cyclical change in affect; others show pronounced change; and the shape of the change varies. "My luteal phase is hard" and "my peri-menstrual days are hard" describe two different patterns, not two names for the same thing.

One more thing worth noting

A 2026 study in Archives of Women's Mental Health examined a large cohort of women who had experienced adverse mood on oral contraceptives.[5] The finding was that this mood response was associated with elevated genetic risk for depression and greater vulnerability to other hormone-sensitive mood patterns. The researchers suggest that a pronounced mood response to a contraceptive pill is a signal (evidence of a pre-existing biological sensitivity to hormonal fluctuation) rather than a side effect to push through. It is information, not just a complaint.

I am not drawing any clinical conclusion from this, and the study does not either. The finding reframes what has historically been dismissed: across the cohort studied, mood change during oral contraceptive use correlated with a pre-existing biological vulnerability, rather than being a side effect without further meaning. It is a finding worth knowing about.

The reframe, not the fix

I notice I am resistant, again, to ending an essay like this with a recommendation. The women MoMo works with do not need to be told to track their cycles, or to plan their weeks around their luteal phases, or to rest more before their period. Some already do. Some do not want to. The value of this research is not in the prescription it enables.

The value is in the naming. When the week before your period feels harder (when you are surprised by how much a small thing cost you, when the gap between what happened and how it landed seems inexplicably wide) there is now a precise, documented account of what is happening. A sensitivity. A biological pattern that has been measured and named.

That is not a moral event. It is a pattern. And patterns, once visible, are something you can hold alongside yourself rather than turn against yourself.

The kind of companion that holds a thread across days and weeks (remembering which patterns keep returning, reflecting them back without judgment) is what MoMo was built to be. But that is a footnote to the essay. The essay is the pattern. The pattern is real.

If this resonates in a painful way (if you're in distress or crisis), please reach out: Mind Sweden 90101 | Samaritans UK 116 123 | your local crisis line.

References

Andersen, E. H., Nagpal, A., Eisenlohr-Moul, T. A., & Gordon, J. L. (2024). A novel method for quantifying affective sensitivity to endogenous ovarian hormones. Psychoneuroendocrinology, 167, 107095. PMID: 38896987.
Farris, S. G., DiBello, A. M., Altman, B. R., et al. (2025). Difficulties with emotion regulation amplify perimenstrual emotional distress and cigarette craving. Psychology of Addictive Behaviors, 39(3), 311–319. PMID: 40193449.
Peters, J. R., Schmalenberger, K. M., Eng, A. G., et al. (2025). Dimensional Affective Sensitivity to Hormones across the Menstrual Cycle (DASH-MC): A transdiagnostic framework for ovarian steroid influences on psychopathology. Molecular Psychiatry, 30(1), 251–262. PMID: 39143323.
Pletzer, B., Hausinger, T., Thoms, N., Gierg, C., & Beltz, A. M. (2026). Menstrual cycle variations in stress vulnerability and sociability relate to mental health symptoms and libido. NPJ Women's Health, 4(1), 18. PMID: 42004752.
Kiewa, J., Lind, P. A., Hickie, I. B., et al. (2026). Poor mood after oral contraceptive use and vulnerability to hormone-sensitive mood patterns. Archives of Women's Mental Health, 29(3), 71. PMID: 42090064.
Bencker, C., Gschwandtner, L., Nayman, S., et al. (2025). Progestagens and progesterone receptor modulation: Effects on the brain, mood, stress, and cognition in females. Frontiers in Neuroendocrinology, 76, 101160. PMID: 39515587.