O Grandma is stuck in traffic. The red cow has been slaughtered. It is raining on the farm. Aunt Flo has arrived. The painters are in the staircase. It’s strawberry season again!
People become surprisingly creative when it comes to disguising something that is commonly regarded as disgusting and embarrassing. It could be so simple. Two words, no glossing over: I bleed. “Where exactly?!” could be the legitimate—yes, somehow justified—question. Fortunately there are a few alternatives to pre-empt such misunderstandings: I have my period. I am menstruating. Blood comes from my vagina.
To be precise, on average, a menstruating person loses just under 90 milliliters of blood per cycle. That could fill roughly nine vials, like the ones used for blood draws. Or half a plastic cup in which urine is usually collected for testing. Visualizing menstrual blood in vessels that are later sent to the lab may feel unfamiliar.
Hundreds of proteins, cells and hormones teem in menstrual blood – and provide valuable information about the body
With fluids like venous blood, urine or saliva, we know the game: we remove them from our bodies to test them for inflammations and diseases. Menstrual blood, however, ends up directly in the trash or wastewater. Could we be overlooking a valuable and easily accessible resource?
Menstrual blood is different
Menstrual blood is not the same as venous blood. For during a period, parts of the uterine lining are shed as well. This lining builds up at the start of each cycle so that a fertilized egg can settle in comfortably. If that does not happen, the body expels the tissue again through weak and strong, short and long contractions. What cannot be seen when looking at underwear is that hundreds of proteins, cells and hormones teem within it. To laypeople, under a microscope they might resemble fried eggs or knotted swimming noodles.
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In them, more and more experts now see huge potential for medical research. Depending on the concentration of these proteins and cells in menstrual blood, they can reveal information about the state of a body. They then serve as biomarkers, markers for detecting and treating diseases. If menstrual blood were studied specifically, gynecological diseases and even tumors could be detected earlier and without extensive invasive interventions.
That is what a research team at the Swiss Federal Institute of Technology in Zurich says as well, which recently brought attention to an unusual menstrual pad. The principle behind it is similar to a COVID-19 rapid test: the person menstruates onto the pad and analyzes the integrated test surface using differently visible color bands. It can also be done with an app. Depending on the intensity of the bands, it indicates whether certain protein values in the blood are elevated. That should provide hints of possible inflammations or cancers. After an initial successful feasibility study, a trial is currently underway to test how well the technology performs in everyday life.
Indicator for Diseases
The Swiss approach is not new. Already in early 2024, a pad was approved by the US Food and Drug Administration that collects menstrual blood in a test stick. Here the goal was not to detect gynecological diseases, but to measure blood sugar, specifically the protein Hemoglobin A1c. This shows how high the average blood sugar level over the last two to three months was—a key parameter for diagnosing diabetes.
But can proteins reliably inform about gynecological diseases such as endometriosis? Sylvia Mechsner, head of the Endometriosis Center at Charité in Berlin, is skeptical. The protein CA-125, for example, which is often associated with endometriosis but also with ovarian or cervical cancer, is reliably elevated when cysts are present or endometriosis is quite advanced. If the value is normal, it does not necessarily rule out the disease.
Nevertheless, menstrual blood does have potential to provide indications of endometriosis, says Mechsner. She places hope in the analysis of stem cells contained within it. Endometriosis is a widespread condition in which tissue similar to the uterine lining grows outside the uterine cavity.
As with many other experts*, Mechsner assumes that endometriosis causes stem cells from the uterus to detach as they move and migrate to other parts of the body, for instance the abdominal cavity or the ovaries. There they settle and form the typical endometriosis foci that respond to hormones and often trigger severe pain.
These stem cells are also washed out with menstrual blood. There is now scientific evidence that the stem cells from healthy individuals differ from those with endometriosis. Yet diagnostic tests based on these differences are still not on the market. How can that be?
Too little funding for medical research
The answer is multifaceted and also relates to a central problem: diseases that affect almost only people with a uterus have low priority in medicine. According to a Nature-focused USA study, migraines, endometriosis and anxiety disorders—conditions disproportionately affecting women—receive far less funding relative to their burden on the population than other diseases.
This leads to even promising findings—such as those from pilot studies with menstrual blood—not being translated into large, reproducible studies. Because the money is missing. And thus the prerequisite for developing clinical tests.
Women, in fact, were systematically excluded from clinical studies until the early 1990s. Even today, people who are not cis men are far less represented in them. Insights into disease symptoms or medication side effects are therefore primarily based on male bodies. As a result, globally, women spend on average 25 percent more of their lives in poor health than men. Government funding programs aim to change this and strive to close the so-called gender data gap in clinical research.
Companies see a market gap
Why does my bleeding hurt so much? Why does it come so irregularly? Many people affected by gynecological diseases search for answers to such questions for years in vain. No wonder that companies that loudly and confidently promise to have the answers are booming.
“There are now several startups that aggressively market overpriced tests without enough scientific data,” criticizes endometriosis researcher Sylvia Mechsner. As an example, she cites a German startup that since 2022 has been developing a test that, from menstrual blood, among other things, should determine hormone levels, promising to deliver information about fertility or early menopause within a few days.
Whether menstrual blood can indicate fertility is something science cannot yet prove or disprove. One researcher who has been dealing with this question for about 15 years is Renate van der Molen, a medical immunologist from Radboud University in the Netherlands. In her group, she studies immune cells from menstrual blood and compares them with tissue samples from the uterine lining.
Her studies show that cells obtained from menstrual blood bear a clear resemblance to those from tissue samples. If this is confirmed in other studies, invasive procedures for detecting inflammations or diseases of the uterus may no longer be strictly necessary.
In regions where access to gynecological preventive care is limited, this could mean a major relief for those affected. Many gynecological diseases can currently only be diagnosed with invasive procedures. This leads to many people living with uncertainty for much of their lives.
Lack of knowledge prevents further research
Critics of menstrual blood samples argue that the amount and composition of the blood vary greatly from person to person: Some periods resemble a waterfall, with XXL tampons overwhelmed by it. Others flow like a leaky faucet and leave stains in their underwear for more than a week.
Renate van der Molen also says more studies are needed to examine the fluctuations across different menstrual cycles and their effects on the cell samples. She adds, though: “Because of these uncertainties, necessary studies are not funded, and it is very difficult for researchers in this field to obtain funding. It’s sadly a vicious circle.”
Dank besonderer Stammzellen erneuert sich die Gebärmutterschleimhaut jeden Monat innerhalb weniger Tage, ohne dass dabei eine Narbe entsteht
That is also what researchers in Australia recognized in 2017 when they published a study on the effect of menstrual blood on wound healing. They introduced human skin cells into a Petri dish, pierced the cell layer, and filled it with plasma from menstrual blood. When they returned a day later, the holes had disappeared.
The same experiment with venous blood plasma produced markedly different results: Only 40 percent of wounds were healed after 24 hours. Whether their observations could revolutionize wound healing remains unanswered. Funding for further studies was lacking.
There are plausible explanations for why menstrual blood might accelerate regenerative processes. No, the magical or sacred effect that some spiritual circles invoke has no place here. Although it is almost miraculous what the uterine lining can do: thanks to its special stem cells, which divide rapidly and multiply, it regenerates itself every month within a few days, without leaving a scar.
Bisher unterschätztes Potenzial
Nevertheless, menstrual blood played little to no role in research until about ten years ago. An analysis from 2022 shows that a large portion of publications on stem cells in menstrual blood appeared only since 2018. The fact that research began to take an interest in the topic is largely thanks to the efforts of feminist movements. In recent years, they have pushed menstruation further into public discourse.
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In Spain, for example, people with menstrual discomfort have legally up to five sick days per month since 2023. In many other countries, the value-added tax on menstrual products has been abolished. In Scotland, since 2022 all public institutions are required to provide them for free.
Faster to Endometriosis Diagnosis
Yet from the first symptoms to the diagnosis of endometriosis, it still takes up to twelve years. Affected individuals report that doctors often dismiss their complaints as menstrual pain and do not deem elaborate examinations necessary. “This has to get better!” four young medical researchers from Linz write on their website.
They are working on a rapid test for endometriosis that focuses on the RNA signatures of cells from menstrual blood. They examine which genes are active in a cell and to what extent. From this, one can read how cells respond to stimuli or diseases. It is currently being tested in a clinical study.
“We want women who have a strong suspicion of endometriosis not to depend on doctor visits anymore,” says Peter Oppelt, director of the University Clinic for Gynecology and Obstetrics in Linz and the project leader. The test should be freely accessible and affordable. He cannot yet name an exact price on request.
