The Science Behind Premenstrual Syndrome

It's a regular Tuesday afternoon. Your colleague makes a harmless joke, and instead of laughing, you feel an overwhelming urge to cry. Your shirt feels tight, your back aches, and you've demolished an entire family-sized meal without realizing it. You check your calendar, and it clicks: your period is due in four days.

Sounds familiar right? 

Chances are that as a woman, you've experienced this scenario or something similar. Welcome to the world of premenstrual syndrome, better known as PMS, a condition that affects up to 90% of women to some degree.

Despite how incredibly common PMS is, many people still don't understand why it happens. We've normalized the symptoms without explaining the science. Today, I want to change that. Let's dive into what's actually happening in your body during those days before your period and why it makes you feel like you're experiencing a monthly personality change.

PS: We're using a 28-day cycle as a reference point, but you can adjust these timelines to match your own cycle length.

The Hormonal Drop

Your menstrual cycle is a carefully choreographed dance between hormones. In the first half (the follicular phase), estrogen gradually rises. Around day 14 of a 28-day cycle, you ovulate. In the second half (the luteal phase), progesterone joins in, and both hormones reach impressive heights. This is when you typically feel your best.

Then it gets interesting.

About a week before your period, if you're not pregnant, both estrogen and progesterone drop from their peak levels to nearly nothing in just days. This is not a gentle descent; it's like your hormones jumping off a cliff.

Remember that these aren't just reproductive hormones; they affect virtually every system in your body, especially your brain. When they drop suddenly, it's like pulling the rug out from under your entire biological system.

Your Brain Chemistry Gets Disrupted

Estrogen and progesterone have direct access to your brain's neurotransmitter systems, particularly serotonin and GABA.

Estrogen and Serotonin: When estrogen levels are healthy, it boosts serotonin production. Serotonin is your mood stabilizer, keeping you feeling balanced and content. When estrogen crashes, serotonin availability drops with it, leading to irritability, sadness, anxiety, and intense food cravings (especially for carbs, which temporarily boost serotonin).

Progesterone and GABA: Progesterone breaks down into allopregnanolone, which acts on GABA receptors. GABA is your brain's chill pill; it's the main calming neurotransmitter. When progesterone is high, you feel relaxed, maybe even a bit sleepy. When it suddenly drops, you lose that calming effect, which can trigger anxiety, restlessness, and sleep disturbances.

Essentially, you're experiencing neurochemical withdrawal. Your brain had adjusted to higher levels of these mood-stabilizing influences and is now scrambling to cope with their absence.

The Inflammation Response

When progesterone drops, it triggers inflammation in your body. Prostaglandins (inflammatory compounds) gear up to help your uterus contract and shed its lining. But they also cause pain, breast tenderness, and headaches and can affect your mood through brain inflammation.

Some people produce more prostaglandins than others, which is why PMS severity varies so much. It's not about having a low pain threshold or being dramatic; it's about biochemistry and individual differences in inflammatory responses.

Water Retention and Fatigue

As progesterone levels shift, your body can retain 1-2 L of water. This fluid redistribution causes bloating and breast swelling and can contribute to headaches. It's not real weight gain, but it certainly feels uncomfortable.

You're also genuinely more tired. Progesterone has sedating properties, and as it drops, your sleep patterns get disrupted. Lower serotonin levels affect melatonin production (melatonin is made from serotonin), leading to poorer sleep. Poor sleep then exacerbates every other PMS symptom, creating a vicious cycle.

The Blood Sugar Connection

Progesterone increases insulin resistance, making your cells less responsive to insulin. As progesterone drops, your blood sugar regulation becomes erratic. This is why you crave sweet or carbohydrate-rich foods. Your body is seeking quick energy to stabilize blood sugar.

Those cravings aren't a failure of willpower; they're your body trying to maintain metabolic balance. However, giving in to processed foods and an unhealthy diet can create blood sugar spikes and crashes that worsen mood swings and fatigue.

When PMS Becomes PMDD

About 5-8% of women experience premenstrual dysphoric disorder (PMDD), a much more severe condition involving the same hormonal mechanisms but with dramatically intensified symptoms: severe depression, debilitating anxiety, extreme irritability, and even suicidal thoughts.

PMDD is not "bad PMS." It's a distinct condition that significantly impairs quality of life and requires medical intervention. If your symptoms regularly interfere with work, relationships, or daily functioning, talk to a healthcare provider.

What Actually Helps

Track your cycle. When you know PMS is coming, you can plan demanding tasks for other times and be gentler with yourself.

Stabilize blood sugar. Eat regular meals with protein, healthy fats, and complex carbohydrates. Focus on leafy greens, nuts, seeds, whole grains, and legumes; they contain magnesium and B6, which help produce serotonin and regulate hormones.

Move your body. Exercise increases endorphins and helps regulate serotonin. Even a 20-minute walk makes a significant difference.

Prioritize sleep. Maintain consistent bedtimes, keep your room cool and dark, and limit screens before bed.

The Bottom Line

You're not weak or "too emotional." You're experiencing a legitimate physiological event involving your endocrine, nervous, immune, and metabolic systems. Your hormones affect every organ in your body, especially your brain.

PMS is real. The science behind it is complex. And you deserve both understanding and effective treatment options.