Four Phases, One Conversation: What Your Cycle is Really Doing…

We all know periods... but what is your body doing the other three weeks of the month? Your period accounts for around a fifth of your menstrual cycle, leaving the remaining weeks a little more unknown. The answer is a month-long conversation between your brain and ovaries, conducted entirely by hormones. Here’s a quick guide to all four phases and what each one can tell you:  

The Menstrual Phase  

The first day of your menstrual cycle starts with your period, which itself is the result of a hormonal withdrawal. When the previous cycle ends without pregnancy, the levels of the hormone progesterone fall. Without progesterone to support it, the uterine lining breaks down and is shed, producing the bleeding we recognise as a period, which averages around 30-40ml per cycle (Thiyagarajan et al.).  

The uterus then produces prostaglandins, molecules that make the uterine muscles contract to help push the lining out. These contractions cause the hallmark cramps experienced during menstruation. It is also why ibuprofen is more effective for period pains than paracetamol, as ibuprofen directly targets the production of these nasty prostaglandins. Prostaglandins can act on muscles all throughout the body, explaining why cramps often arrive alongside an unsettled stomach. Meanwhile, oestrogen and progesterone are at their lowest, explaining why a crash in energy here is biology, not “laziness” (Thiyagarajan et al.).  

Period pain is uncomfortable, but it should always be manageable. Severe, debilitating pain isn’t something you should simply put up with. It could be a sign of a condition like endometriosis, which affects 1 in 10 menstruators and takes on average around 9 years to diagnose (Endometriosis UK).  

The Follicular Phase  

Did you know you are born with around 1 to 2 million immature eggs, yet only 400 will ever be ovulated (Center for Young Women’s Health).  

The follicular phase is where that selection happens, and it starts alongside your period. While the uterus sheds its lining, the brain starts to release another hormone called Follicle Stimulating Hormone (FSH) which travels to the ovaries and then prompts a group of follicles (fluid filled sacs containing an egg) to start growing. These follicles grow in competition, until one becomes dominant and the rest break down. This “winning” follicle produces oestrogen which rebuilds the uterine lining that was shed during your period (Thiyagarajan et al.). However, oestrogen does more than just this: in the brain it increases serotonin signalling, whilst in the skin it supports collagen and hydration (Thornton 265). This crucial information explains why many people notice their energy, mood, and skin improving as the phase goes on.  

This phase is also the reason cycle length differs so much. The time it takes for a follicle to mature differs between people, and from month to month, which is why a 28-day cycle is far from universal (Fehring et al. 384). It is also the reason that a stressful few weeks can throw off your cycle, as stress hormones lower the brain’s signalling to the ovaries, so the follicle takes longer to mature.  

Ovulation 

This is the moment that your whole cycle has been building towards, the point where the internal conversation reaches its loudest. Oestrogen from the dominant follicle stays high for around two days, whilst the brain responds with a sudden surge of another hormone (promise this is the last one!), luteinising hormone (LH). This causes the all-important follicle to rupture, releasing its egg into the fallopian tube.  

Sometimes this can be physically felt through a brief one-sided twinge in the lower abdomen, called mittelschmerz (German for “middle-pain”) (Harvard Health). The egg survives here for around 12 to 24 hours, but the fertile window is considerably longer than this, as sperm can survive for up to five days. 

The Luteal Phase 

With the egg released, the ovaries must now do most of the talking. A surge of LH transforms the emptied follicle into a temporary structure called the corpus luteum, producing progesterone, which prepares the uterine lining for the implantation of a fertilised egg. After a cycle led mainly by oestrogen, progesterone now takes over (Thiyagarajan et al.). It nudges your resting body temperature to a slightly higher level, which some wearables (such as Oura Ring or Apple Watch) use to confirm ovulation has occurred.  

These final days are when premenstrual syndrome (PMS) symptoms tend to appear, from fatigue to bloating and mood changes. Current evidence suggests PMS isn’t caused by abnormal hormone levels at all, but individual sensitivity to these shifts, which is why two people with identical hormones can feel completely different (Modzelewski et al. 2).  

Then, if no pregnancy occurs, the corpus luteum breaks down. Progesterone and oestrogen fall, and that withdrawal triggers your next period, starting the whole conversation again. This phase is usually more consistent at around 12 to 14 days long, so if your cycle length changes, it’s almost always the follicular phase that has caused this (Fehring et al. 384).  

Four phases, one conversation, and a body that tells you far more than you’d think.   

References 

‘Endometriosis UK Release New Report Highlighting Alarming Increase in Endometriosis Diagnosis Times.’ Endometriosis UK, https://www.endometriosis-uk.org/news/endometriosis-uk-release-new-report-highlighting-alarming-increase-endometriosis-diagnosis (Accessed 1st Oct. 2026) 

Fehring, Richard J., et al. ‘Variability in the Phases of the Menstrual Cycle.’ Journal of Obstetric, Gynaecologic and Neonatal Nursing, vol. 35, no. 3, 2006, pp. 376-84 https://www.jognn.org/article/S0884-2175(15)34376-8/abstract (Accessed 8th Oct. 2026) 

‘How Many Eggs Does a Woman Have in Her Lifetime?’ Center for Young Women’s Health, Boston Children’s Hospital, 3 Sept. 2018, https://youngwomenshealth.org/askus/how-many-eggs-does-a-woman-have-in-her-life-time/ (Accessed 8th Oct. 2026) 

‘Mid-Menstrual Cycle Pain (Mittelschmerz).’ Harvard Health, 10th Feb. 2024, https://www.health.harvard.edu/a_to_z/mid-menstrual-cycle-pain-mittelschmerz-a-to-z (Accessed 8th Oct. 2026) 

Modzelewski, Stanisław, et al. "Premenstrual Syndrome: New Insights into Etiology and Review of Treatment Methods." Frontiers in Psychiatry, vol. 15, 2024, article 1363875, https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2024.1363875/full. (Accessed 8th Oct. 2026) 

Thiyagarajan, Dhanalakshmi., et al. ‘Physiology, Menstrual Cycle.’ StatPearls, StatPearls Publishing, 27th Sept. 2024, https://www.ncbi.nlm.nih.gov/books/NBK500020/ (Accessed 8th Oct. 2026) 

Thornton ‘Estrogens and Aging Skin.’ Dermato-Endocrinology, vol. 5, no. 2, 2013, pp. 264-70, https://pmc.ncbi.nlm.nih.gov/articles/PMC3772914/ (Accessed 8th Oct. 2026)