Knowing Your Cycle: The Biology That Shapes You

Written By Charlotte Farrar

What is the menstrual cycle? How does the menstrual cycle affect your body? What drives these changes?

Most of us were given a quick textbook explanation of the menstrual cycle in school: something about eggs, womb linings, and bleeding. For many, that’s where the conversation stopped. The reality is much more interesting (and useful). Your cycle is controlled by hormones (chemical messengers that rise and fall in predictable patterns), which impact how your body feels in a myriad of ways.  

Unfortunately, what we don’t learn in school gets pieced together later from whispers in classrooms, advice from relatives, and endless social media “wellness” tips. For those experiencing their first period, this lack of clear information can be overwhelming. That’s why we’ve pulled everything together in this blog: to explain, in plain language, what’s actually happening in your body during each stage of the menstrual cycle. By the end, you’ll not only understand the biology, but also how to recognise what your body is telling you, and how to work with your cycle instead of against it.

The Menstrual Cycle 101

According to the NHS UK, menstruation usually occurs between the ages of 12 and 51 and the average length of a cycle is 28 days. Day 1 is the first day of your period, and the last day is the day before your next period begins. The different stages of your menstrual cycle are divided into menstrual, follicular, ovulation and luteal. The table below outline the biological ins-and-outs of the menstrual cycle, paying attention to timescales, hormonal changes, and the different reproductive organs: 

What Really is ‘Normal’?

The table above is typical of a 28-day cycle with 3-7 days of bleeding. However, digital health data shows that only 13-15% of menstruators have a “textbook” 28-day cycle. Recent large-scale studies confirm that a healthy menstrual cycle can be between 24 and 38 days long, with regularity defined as less than 7 to 9 days variation between cycles*. Variation is especially common among younger menstruators and those approaching menopause. Using a period tracking app, such as Stardust or Clue, is personalised and can help you keep track of which menstrual stage you are in.  

While variation is ‘normal’, an irregular period occurs when your period falls outside the parameters of a healthy menstrual cycle. Several factors influence your cycle including lifestyle factors such as stress or more severe medical issues such as endometriosis and PCOS. If you experience signs of irregularity, it’s important to consult a doctor. Warning signs include:

  • Missing more than three periods in a row.

  • Bleeding through more than one tampon or pad per hour.

  • Periods that last longer than a week.

  • Periods cycles that aren’t within 24-38 days.

  • Severe cramping, vomiting, or pain.

  • Bleeding between periods.

  • Heavier or lighter bleeding than normal.

  • Anaemia symptoms (fatigue, dizziness and shortness of breath).

This list is not exhaustive, and there is a growing consensus that any menstrual bleeding which negatively affects physical, emotional, social, or material quality of life is considered abnormal, regardless of volume. This is an impact-based definition and reinforces that no two cycles are the same. “Regular” is ultimately what is regular for you.

How Hormones Affect Your Body

Understanding the biology of your cycle can be empowering and important for your health. However, it’s equally important to recognise that the menstrual cycle is more than just the days you bleed. Because hormones fluctuate throughout your entire cycle, you can expect changes in your hair, skin, digestion, energy levels, and libido throughout. Each stage of your cycle, and the symptoms they typically bring, can be understood as seasons within our bodies. Awareness of the changes inside your body as the seasons progress can help you to manage symptoms or avoid triggers that worsen them. For how your menstrual cycle and its seasons affect your mind, see ‘Owning Your Cycle: The Emotions That Guide You.’ 

During the menstrual stage, winter has fallen and you and your hormones are at their lowest (literally). To help expel the uterus lining, hormone-like substances called prostaglandins are produced to trigger contractions. These contractions can be painful and cause cramps. In general, higher levels of prostaglandins are associated with more intense cramps. However, more serious conditions like endometriosis and pelvic inflammatory disease can contribute to and worsen cramps. Other symptoms during the menstrual phase also include:

  • Tender breasts

  • Muscle aches

  • Joint pain

  • Headaches

  • Acne

  • Diarrhoea or constipation

With the loss of blood, your body is working extra hard. So, as you would in winter, now is the time to schedule in down-time and self-care. 

During the follicular phase, bleeding ends and winter turns to spring. Oestrogen starts to rise and with it comes an increase in physical energy and strength. You may notice clearer skin and better sleep. This would be a great time to push yourself in workouts. 

During ovulation, oestrogen is at its highest and so is the summer sun! You are hormonally primed to look and feel your best. This is your body’s ‘peak performance’ window. Inflammation is low, your face is symmetrical, and your skin is glowing! Testosterone is also up, meaning you are on top of your game physically and quick on your feet. Ovulation is your most fertile window, so unironically, you can also expect a high libido. 

Lastly, during the luteal phase, your hormones are crashing, signalling to your brain to restart the cycle. Much like the transition from summer to autumn, your energy levels and glow are slowly decreasing. Now, it is common to experience Premenstrual Syndrome (PMS) symptoms. Many PMS symptoms are emotional, but the most common physical ones include:

  • Fatigue

  • Breast tenderness

  • Headaches

  • Acne

  • Changes in appetite or food cravings. 

  • Bloating

PMS is a broadly accepted and normalised part of a menstruator’s life, even though little is known about what causes it. During this time, prioritise rest and balanced meals.. Tracking your cycle can help you spot patterns so PMS doesn’t take you by surprise. If lifestyle adjustments do not provide relief, or symptoms significantly affect your daily life, talk to your NHS GP. 

The Bottom Line

No two cycles are the same and “normal” symptoms feel different for everyone. What is important is recognising your own cycle pattern and symptoms, understanding what your body is telling you - through winter, spring, summer and  autumn - and knowing when to seek support. 

*Source: Rosen Vollmar, A.K., Mahalingaiah, S. and Jukic, A.M. (2025). The Menstrual Cycle as a Vital Sign: A Comprehensive Review. F&S Reviews, 6(1), p.100081. doi: https://doi.org/10.1016/j.xfnr.2024.100081.

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Charlotte Farrar
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Owning Your Cycle: The Emotions That Guide You