Cycle science

Where period cramps come from

By My Body's BFF Published August 23, 2026 Read 7 min

Some cramping is expected, and it has a specific cause. Pain that keeps you home, or that has been getting worse year on year, is a different thing. The difference matters, and most women are never told what separates the two.

The short answer

As the lining of your uterus breaks down, it releases prostaglandins. These make the uterine muscle contract so the lining can be shed. Strong contractions briefly squeeze the blood vessels running through that muscle, reducing its own oxygen supply, and that is what registers as cramping.1

Women with more painful periods tend to have higher prostaglandin levels in menstrual fluid.2 The pain is not imagined and it is not a low pain threshold. It is a measurable difference in the chemistry.

That explains ordinary cramps. It does not explain all period pain, and the difference is the reason this article exists.

What ordinary period pain tends to look like

  • Begins shortly before bleeding starts, or with it
  • Strongest in the first day or two, easing within one to three days
  • Cramping low in the abdomen, sometimes spreading to the lower back or thighs
  • Eases with heat
  • Started within a couple of years of your first period
  • Roughly the same each cycle rather than escalating year on year

That pattern is pain from prostaglandins, with nothing underlying it.

The reframe. "Normal" here does not mean "as much pain as you happen to have". It means pain with a known mechanism, a predictable shape, and an end. Anything outside that shape is a question, not a verdict about your tolerance.

Where ordinary ends

Not all period pain follows that shape, and the differences are learnable.3

Signs that point away from ordinary cramping:

  • Pain that stops your life. Missing work, school or plans most cycles.
  • Pain that is getting worse over years rather than staying roughly constant.
  • Pain outside your period, in the middle of your cycle or most of the month.
  • Pain during or after sex.
  • Very heavy bleeding, flooding, large clots, or soaking through protection hourly.
  • Cyclical bowel or bladder pain, pain on opening your bowels around your period.
  • Pain that started years after your first period rather than close to it.
  • Vomiting or fainting with the pain.

None of these means anything on its own. What they have in common is that they sit outside the ordinary shape, and pain outside that shape is not something to talk yourself out of.

The sentence worth carrying

Period pain that stops your life is not normal, and it is not something to endure quietly.

Women are frequently told that severe periods are simply part of being a woman. Being dismissed is not the same as being fine, and pain that takes days out of your life every month is worth more than being told to get used to it.

What helps with ordinary cramps

  • Heat. Topical heat has reasonable evidence behind it.4
  • Movement, at whatever level is available. Gentle activity helps some women, though not during the worst hours.
  • Tracking the pain. Not because it reduces it, but because a record of when pain lands, how severe it is and what else it comes with is far more useful than memory.

Stop running on memory.

My Body's BFF tracks pain and symptoms alongside your cycle. After a few cycles you can see for yourself which days it lands on and how bad it got, instead of trying to reconstruct it from memory. The app does not diagnose anything.

Download the app

The takeaway

Ordinary period pain has a mechanism, a shape and an end. Prostaglandins make the uterus contract, the contractions cause cramping, and it eases within a few days.

Pain that falls outside that shape, that escalates, or that takes days out of your life, is not the same thing. Knowing which one you have is the point, and it is not something you have to keep quiet about. (See also: what is actually normal in a cycle.)

FAQ

Is period pain normal?

Some is. As the lining of the uterus breaks down it releases prostaglandins, which make the uterine muscle contract to shed it. Strong contractions briefly reduce blood flow to the muscle, and that is what produces cramping. This kind of pain typically begins within a couple of years of your first period, starts shortly before or with bleeding, and eases within one to three days. Pain that stops you living your normal life is not in this category.

How much period pain is too much?

A useful threshold is function rather than a pain score. Pain that regularly keeps you home from work or school, pain that makes you vomit or faint, or pain that has been getting worse over years sits outside the ordinary pattern. Pain you can work around with a hot water bottle sits in a different category.

Sources

  1. Iacovides S, Avidon I, Baker FC. What we know about primary dysmenorrhea today: a critical review. Hum Reprod Update. 2015;21(6):762–778.
  2. Dawood MY. Primary dysmenorrhea: advances in pathogenesis and management. Obstet Gynecol. 2006;108(2):428–441.
  3. Zondervan KT, Becker CM, Missmer SA. Endometriosis. N Engl J Med. 2020;382(13):1244–1256.
  4. Igwea SE, Tabansi-Ochuogu CS, Abaraogu UO. TENS and heat therapy for pain relief and quality of life improvement in individuals with primary dysmenorrhea: a systematic review. Complement Ther Clin Pract. 2016;24:86–91.

This article is for general education. It is not medical advice and it was not written by a doctor. Everything above comes from the published research listed here, and none of it can tell you what is happening in your own body. For that, speak to a qualified healthcare provider.