The blood we were taught to fear.

01

What it is, scientifically

Menstruation is the shedding of the endometrium, the inner lining of the uterus, which thickens each month in preparation for potential implantation. When implantation does not occur, estrogen and progesterone levels drop, and the body releases the lining. The process is triggered by prostaglandins, hormones that cause the uterine muscle to contract. This is what creates cramping.

Menstrual blood is not the same as circulatory blood. It is a complex fluid: blood, endometrial tissue, mucus, vaginal secretions. And something else, which we will return to in the final section.

Dysmenorrhea, painful menstruation, affects between 50 and 90 percent of women of reproductive age. It remains one of the most undertreated pain conditions in medicine.[1] Endometriosis, in which endometrial-like tissue grows outside the uterus, affects approximately 1 in 10 women and carries an average diagnosis delay of 7 to 10 years.[2] In 2015, the American College of Obstetricians and Gynecologists declared that the menstrual cycle should be treated as a fifth vital sign, a monthly marker of overall health.[3] Most women have never been told this.

02

What it has meant, across cultures and through history

If medicine has spent two centuries treating the period as a problem, the longer human record is far more complicated. The same blood that clinicians have historically pathologized was, in other times and places, considered one of the most powerful substances a human body could produce. What runs through almost every culture, across every direction, is that menstrual blood was recognized as significant. The disagreement was about what kind of significance.

In ancient Rome, Pliny the Elder wrote in his Natural History that a menstruating woman could cause crops to fail, wine to sour, mirrors to fog, and iron to rust.[4] She was, in his account, a walking contamination. The Hebrew Bible's Leviticus chapter 15 established the niddah laws: a menstruating woman was ritually impure for seven days, and anyone or anything she touched shared that impurity. In medieval Christian Europe, women were barred from entering churches and from handling food during menstruation. Church doctrine connected the blood directly to Eve's transgression.

The isolation could go much further. In parts of rural India and across western Nepal, a practice known as Chaupadi required menstruating women to leave the household entirely, living in small stone huts or cowsheds for the duration of their period. They were forbidden from entering homes, touching food, approaching cattle, or visiting temples. Contact, it was believed, would bring misfortune to the household. Chaupadi was declared illegal in Nepal in 2005, then recriminalized with explicit penalties in 2017, following a series of documented deaths: women dying from hypothermia, snake bites, smoke inhalation in sealed huts during winter. Human Rights Watch documented the practice affecting hundreds of thousands of women still as recently as the 2020s.[5] Variations of menstrual isolation persist across parts of Odisha, Rajasthan, and other regions of India today.

The logic across all of these systems (the Roman field, the medieval church, the Nepali hut) is identical: the bleeding woman is dangerous. She must be contained. Removed from the center of communal life.

But not everywhere. And not always.

In many indigenous traditions of North America, menstruation was called "moon time" and recognized as a period of heightened spiritual perception. Women withdrew from communal labor not as punishment, but as acknowledgment: during these days, proximity to the unseen was considered stronger. The withdrawal was a form of respect, not exile. Among some Apache groups, the first period was marked by the Sunrise Dance, a multi-day ceremony celebrating entry into womanhood. In certain left-hand Tantric traditions in India, menstrual blood, called rakta, was treated as a sacred substance: a concentrated form of Shakti, divine feminine energy. In ancient Egypt, the Ebers Papyrus, one of the oldest surviving medical texts, recorded menstrual blood as an ingredient in healing preparations.

The pattern, across thousands of years and dozens of cultures, is not fear against reverence. It is recognition of power. The cultures that sought to control women coded that power as contamination. The ones that did not coded it as sacred. The blood itself was the same.

03

Why women stop bleeding, and what that costs

That long history of fear had a material consequence: it shaped how modern medicine approached menstruation. As something to manage. Preferably to suppress.

I know this from the inside. I spent seven years on a contraceptive implant, managing the endometriosis pain that had made my own period unlivable. For seven years, I did not bleed. The implant worked. The pain was gone.

What I did not understand, until much later, was what I had also switched off.

The menstrual cycle functions as a vital sign. Its absence does not mean the body has stopped communicating. It means the monthly signal has been silenced. Irregularities that would appear as symptoms have no channel to appear through. The feedback loop is closed. For many women, suppressing the period is a legitimate medical trade-off: for endometriosis, for severe dysmenorrhea, for conditions where the relief is real and the choice is valid.

What is almost never part of that conversation is what the absence removes. When I stopped using the implant, I did not know what my own period looked like, because I had never had an unmedicated adult cycle. I was meeting my body for the first time. What had felt like a solution had also been, quietly, a form of silence.

04

Why it is more powerful than you were told

Here is what medicine is now finding in the thing it spent two centuries managing.

In the early 2000s, researchers began isolating stem cells from menstrual blood. Menstrual blood-derived stem cells, or MenSCs, were found to be distinct from those harvested from bone marrow or umbilical cord: more abundant, shed monthly without invasive procedures, capable of differentiating into multiple cell types. Research published in Journal of Translational Medicine documented their potential across multiple regenerative medicine applications.[6]

More recently, studies on the exosomes these stem cells release, the extracellular vesicles carried in menstrual blood, found that they significantly accelerate wound healing in preclinical models: promoting new blood vessel formation, reducing inflammation, shortening repair time.[7] The body that bleeds carries, within that blood, some of the most regenerative material it produces.

Ancient traditions knew something was there, even before they had language for stem cells or exosomes. What they named as sacred or dangerous, science is now approaching with instruments. The observation that something in this blood mattered was made across thousands of years. The research is only beginning to answer what.

What changes when you stop managing the period and start attending to it is not mystical. The cramps carry information. The timing carries information. The quality of the flow carries information. A body that bleeds is not a body in deficit.

It is a body in conversation with itself. The question is whether anyone taught you to hear it.