I love science, and I love the scientific method. I think that the scientific method is one of the most useful ways of knowing out there. I have devoted my life not only to the study of the science of human evolution and female reproductive physiology, but to increasing science appreciation and literacy in the general public.

So why am I always criticizing it?

Two reasons. First, the process of science can be biased by who performs it.

Second, the results and implications of scientific research can be biased by who tells it.

To demonstrate this, I’m going to tell you a little story about a menstruating nurse.

* * *

Dr. Bela Schick, a doctor in the 1920s, was a very popular doctor and received flowers from his patients all the time. One day he received one of his usual bouquets from a patient. The way the story goes, he asked one of his nurses to put the bouquet in some water. The nurse politely declined. Dr. Schick asked the nurse again, and again she refused to handle the flowers. When Dr. Schick questioned his nurse why she would not put the flowers in water, she explained that she had her period. When he asked why that mattered, she confessed that when she menstruated, she made flowers wilt at her touch.

So, rather than consider the possibility that the nurse was offended that her skills and expertise were being put to use to put someone else’s flowers in water, Dr. Schick decided to run a test. Gently place flowers in water on the one hand… and have a menstruating woman roughly handle another bunch in order to really get her dirty hands on them:

The flowers that were not handled thrived, while the flowers that were handled by a menstruating woman wilted.

This was the beginning of the study of the menstrual toxin, or menotoxin, a substance secreted in the sweat of menstruating women.

* * *

This story begins far before Dr. Bela Schick and his menstruating nurse. Because the kind of bias that produces a doctor who can believe that menstrual toxins exist, and launch a field of study on them based on some wilted flowers (if the story really did happen the way he tells it), did not come from one man alone. The cultural conditioning that has produced the idea that women are dirty, particularly during menses, is quite old. The Old Testament of the Bible claims that women are unclean when they menstruate, and menstrual huts exist in some cultures to separate out menstruating women from the rest of their group.

But some mark the beginning of our misunderstandings of female physiology in European-derived cultures with one book in particular written in the thirteenth century – De Secretis Mulierum, The Secrets of Women. This book was written by a man who claimed to be the monk Albertus Magnus, but was most likely an impersonator (which is why most call the author of De Secretis Mulierum pseudo-Albertus Magnus, or pseudo-Albert).

So here are some winning quotes from this book, which was considered a premier text for several centuries, even though it is likely pseudo-Albertus Magnus never treated women and based much of his work on having dissected a female pig:

“Woman is not human, but a monster.”

Menstruating women give off harmful fumes that will “poison the eyes of children lying in their cradles by a glance.”

Children conceived by menstruating women “tend to have epilepsy and leprosy because menstrual matter is extremely venemous [sic].”

De Secretis Mulierum went through at least eighty editions over several centuries (Rodnite Lemay 1992). While it was not a strictly medical text, it is clear that it was both popular and influential. Do doctors refer to De Secretis Mulierum today? Of course not. But this book, to me, represents a broader cultural understanding that menstruation is dirty, that women are powerful, mysterious, dangerous, and sub-human.

* * *

So back to those menotoxins. Dr. Schick decided there was something nasty in the sweat of menstruating women. Others took up the cause. Soon, people were injecting menstrual blood into rodents, and those rodents were dying (Pickles 1979). Others were growing plants in venous blood from menstruating women to determine phytotoxicity; the sooner the plants died, the higher the quantity of menotoxin assumed in the sample.

What’s worse, the presence of the menotoxin in the female body began to expand beyond menstruation. Any woman who was post-menarcheal and pre-menopausal could be found to have the menotoxin in her system. She could not escape it: some reported that the menotoxin could be found in a woman’s menstrual blood, but also venous blood, sweat, and breastmilk. One case study reports that a mother gave her child asthma because she was menotoxic during pregnancy (Perlstein and Matheson 1936), and several contended that colic was caused by menotoxin in breastmilk (Ashley-Montagu 1940; Perlstein and Matheson 1936).

Not only did the idea of the menotoxin become a ubiquitous menace around any reproductively-aged woman, it began to explain pathology. So the menotoxin, which first was an explanation for the presence of menstruation in women, became a way of diagnosing women as ill… and again, since now all reproductively-aged women could secrete it from any bodily fluid at any time, the state of being female essentially made one pathological.

Soon the idea that the menotoxin indicated specific illnesses began to take hold.

"Dr. Schick and I discussed the possibility that the adult female diabetic out of control, the depressed adult female psychotic, and the adult female in the premenstrual phase secreted some common substance in their sweat." (Reid 1974)

Here, you see premenstrual women compared directly with two pathological conditions: diabetes and psychosis. And all of these relationships, between menstruation and colic, asthma, wilted flowers, are largely observation, case reports, or poorly controlled experiments. When studies do not support the idea of the menotoxin, as with Freeman et al (1934) and two studies cited by Ashley-Montagu (1940) that were not in English, each get dismissed as outliers (even though in Labhardt’s case from Ashley-Montagu, the sweat of men was often as toxic as that of menstruating women).

And this is where I bring it back to my first two points about bias, that science can be biased by the cultural conditioning of those who perform it, and those who tell it. The people who studied the menotoxin really, really wanted to believe in it, to the point that they would ignore negative results and overstate the power of their anecdotes and case studies. The study of the menotoxin spans at least sixty years, maybe ninety depending on which references you consider legitimate, debated in Lancet letters to the editor, and published in several medical journals.

I wish I could say that the menotoxin was dead. But several contemporary hypotheses about the evolution of menstruation still in some way reflect the thinking that menstruation, if not women, is dirty and serves the purpose of expelling toxicity. Clarke (1994) proposed menstruation as a mechanism to expel unwanted embryos. Margie Profet (1993) argued that menstruation helped to expel sperm-borne pathogens, which made men the dirty party. This is why it’s important to recognize that many ideas that seem intuitive to us at first derive from cultural conditioning and bias. (My favorite book on the topic is Emily Martin’s The Woman in the Body (1980).)

Thankfully, the most accepted idea is that menstruation did not evolve at all, but is a byproduct of the evolution of terminal differentiation of endometrial cells (Finn 1996; Finn 1998). That is, endometrial cells must proliferate and then differentiate, and once they differentiate, they have an expiration date. Ovulation and endometrial receptivity are fairly tightly timed, to the point that the vast majority of implantations occur within a three-day window (Wilcox et al. 1999). So it’s not that menstruation expels dangerous menotoxins, but rather that menstruation happens because the endometrium needs to start over, and humans in particular have thick enough endometria that we can’t just resorb all that blood and tissue.

It’s time to dump the idea that menstruation is dirty. It’s blood and tissue that you ended up not using to feed a baby, and that’s all.


*I want to credit one of my favorite courses from college for much of the content related to pseudo-Albertus Magnus: Women’s Studies 106a, Bodies and Boundaries, taught by Prof. Katherine Park at Harvard University. I have no idea if it’s still taught (*cough* it’s been ten years *cough*), but if you are a student there, you are missing out if you don’t take a class with her.

**If you are a historian of science and would like to talk over this material with me, let me know! It would make for a great paper.


Ashley-Montagu M. 1940. Physiology and the Origins of the Menstrual Prohibitions. The Quarterly Review of Biology 15(2):211-220.

Clarke J (1994). The meaning of menstruation in the elimination of abnormal embryos. Human reproduction (Oxford, England), 9 (7), 1204-7 PMID: 7848450

Finn CA (1996). Why do women menstruate? Historical and evolutionary review. European journal of obstetrics, gynecology, and reproductive biology, 70 (1), 3-8 PMID: 9031909

Finn CA (1998). Menstruation: a nonadaptive consequence of uterine evolution. The Quarterly review of biology, 73 (2), 163-73 PMID: 9618925

Freeman W, Looney JM, and Small RR. 1934. Studies on the phytotoxic index II. Menstrual toxin ("menotoxin"). Journal of Pharmacology and Experimental Therapeutics 52(2):179-183.

Martin E. 1980. The woman in the body. Beacon Press, Boston.

Perlstein M, and Matheson A. 1936. Allergy Due to Menotoxin of Pregnancy. Archives of Pediatrics and Adolescent Medicine 52(2):303.

Pickles VR (1979). Prostaglandins and dysmenorrhea: Historical survey. Acta Obstet Gynecol Scand Suppl 87:7-12.

Profet M (1993). Menstruation as a defense against pathogens transported by sperm. The Quarterly review of biology, 68 (3), 335-86 PMID: 8210311

Reid HE (1974). Letter: The brass-ring sign. Lancet, 1 (7864) PMID: 4133673

Rodnite Lemay H. 1992. Womens Secrets: A Translation of Pseudo-Albertus Magnus' de Secretis Mulierum with Commentaries: State University of New York Press.

Wilcox AJ, Baird DD, & Weinberg CR (1999). Time of implantation of the conceptus and loss of pregnancy. The New England journal of medicine, 340 (23), 1796-9 PMID: 10362823