Menotoxin: The Twentieth-Century Hunt for a Menstrual Poison

Pliny the Elder thought it would be hard “to find anything which is productive of more marvellous effects than the menstrual discharge,” and listed soured must, sterile seeds, dimmed mirrors and blunted steel among them.¹ Beliefs of this kind have a long history, traced in our history of menstruation in medicine. This article follows a narrower and much later story: the period, roughly from 1920 to the 1950s, when physicians and pharmacologists tried to turn the old belief into chemistry. They gave the supposed poison a name, “menotoxin,” and spent decades measuring it. It was never found.

Wilting flowers in Vienna

The modern search began with Béla Schick (1877-1967), a pediatrician at the Vienna University Children’s Clinic, later known for the diphtheria test that bears his name.² The story of how he became interested is told in several versions. A widely read retelling has a nurse refusing to put a patient’s bouquet in water because she was menstruating and believed she would make the flowers wilt.³ A Basel dissertation of 1925, written while Schick’s work was still new, describes something plainer: in 1919 Schick observed a woman in whose hands flowers, especially anemones, wilted unusually fast.⁴

According to that account, Schick tried to test the effect. He used other people as controls and repeated the trial at the woman’s next period. Flowers held in a hand covered by a rubber glove, or only breathed on, were not harmed. He reported effects on baking and on yeast in fermentation flasks, though these went sometimes toward slowing and sometimes toward speeding. He called the active substance “Menotoxin,” a name suggested by Groer, and said he could detect it in sweat and blood but not in saliva.⁴ The paper, “Das Menstruationsgift” (“The menstrual poison”), appeared in the Wiener klinische Wochenschrift in May 1920.² Schick closed it by welcoming the survival of the popular belief and thanking ordinary people for holding on to facts handed down by word of mouth.⁴

The historian Martina Gamper, as reported in 2013, judged Schick’s procedure to be anything but scientific, yet noted that his results were not picked apart at first and that a good number of gynecologists felt their views on the toxicity of menstrual blood had been confirmed.²

A poison in every fluid

Others extended the claim quickly. A researcher named M. Frank placed flowers in the milk of menstruating women and reported that they wilted sooner than flowers in other milk, which fed worries about breastfeeding during menstruation.⁵ In Hamburg, Sieburg and Patzschke applied menstruating women’s sweat to animal tissue preparations and pointed to choline as the active agent.⁴⁵

The most energetic investigator was the pharmacologist David Macht. With Dorothy Lubin he published a long “phyto-pharmacological study of menstrual toxin” in 1923.⁶ As summarized in 1940, Macht and Lubin reported that blood serum, blood cells, saliva, sweat, milk, tears and urine from menstruating women all slowed fermentation by yeast, that they harmed protozoa, and that they withered cut flowers; they proposed that the toxin was an oxycholesterol.⁵ Note that Schick himself had said saliva contained none of it.⁴

Macht’s main tool was a “phytotoxic index.” Seedlings of white lupine (Lupinus albus) were grown in a solution containing a test fluid, and their root growth was compared with untreated controls. On this scale normal human blood serum averaged 75 percent and menstrual serum 51 percent, a figure Montagu placed near the sera of patients with pernicious anemia (44), leprosy (47) and trachoma (48).⁵ Menstruation was thus ranked, by a plant assay, alongside serious disease.

The idea kept spreading into clinical explanation. A 1936 case report blamed a child’s asthma on the mother having been affected by menotoxin during pregnancy, and some writers blamed infant colic on menotoxin in breast milk.³ In 1940 M. F. Ashley-Montagu, then in the anatomy department of Hahnemann Medical College in Philadelphia, surveyed the experimental literature in The Quarterly Review of Biology. He reported that, according to his sources, French perfumeries, wine districts and sugar refineries kept menstruating women away from certain work, and he recalled an 1878 exchange in the British Medical Journal about whether menstruating women spoiled curing meat.⁵ His summary concluded: “It would appear that menstruous women are capable of exerting noxious effects upon many living tissues.” He suggested that trimethylamine was the probable agent, and floated the idea that early human societies had observed such effects and built menstrual prohibitions on them, while calling that suggestion “a pure speculation.”⁵

The negative results

The same 1940 review also contains much of the evidence against the theory. Montagu wrote that one researcher had been unable to confirm Schick’s findings, but described him as “the only investigator who has failed to do so.”⁵ That was not accurate even by his own sources. He reported that Freeman and Looney had found no significant difference between menstrual and intermenstrual blood in 22 women, with phytotoxic indices of 53.2 and 53.9 percent, and that Labhardt in Basel had found some men’s sweat as potent as any menstruating woman’s.⁵ The Freeman study was published in 1934 under the title “Menstrual toxin (‘menotoxin’).”⁷

For the finding about men’s sweat, Montagu cited a 1924 paper by Labhardt.⁵ A 1925 dissertation by Alfred Gengenbach, written in Labhardt’s clinic at Labhardt’s request, reports a similar result in detail.⁴ Gengenbach collected sweat from seven hospital patients before and during their periods. He confirmed that the choline content of sweat rose around menstruation, but when he tested men’s sweat by the same method, it acted on a frog heart at an average dilution of 1 in 2,000, the same limit he had found in the sweat of menstruating women. Every attempt he made to show that menstruating women harmed plants failed. He also could not find a single case like the one Schick described. Popular tradition on the subject, he wrote, was for the most part “Irrtum und Wahn” (error and delusion). He proposed describing menstruation as a changed physiological state rather than explaining it by a hypothetical toxin.⁴

Later work pointed to a more ordinary explanation for some of the animal results. In 1953 the gynecologist Bernhard Zondek asked in print whether menstrual blood contained a specific toxin.⁸ By one detailed summary of his paper, he repeated experiments in which menstrual blood injected into rats had killed most of them. With more sterile collection, deaths fell sharply; the same bacteria were cultured from the samples and from the dead animals, and penicillin removed the “toxic” effect. The researchers whose results he was testing, George and Olive Smith, are reported to have answered that penicillin must neutralize the toxin.⁹

In 1958 a study by Burger at the university women’s clinic in Würzburg is described as having disproved the existence of a menstrual poison.² A 2024 thesis argues that this refutation then dropped out of citations, and that the claim returned in a second wave of debate in The Lancet during the 1970s.¹⁰ A letter on “menstrual toxin” appeared there in 1974, and a note titled “The search for ‘menotoxin’” in 1977.¹¹ Kate Clancy, a scientist who studies human evolution and female reproductive physiology, has summed up the literature this way: “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.”³

What was really in menstrual fluid

Menstrual fluid does contain biologically active substances. They were simply not the poison Schick had imagined. By 1960 Vernon Pickles and a colleague were writing about a substance in menstrual fluid that made smooth muscle contract, “provisionally named the ‘menstrual stimulant,’” which they thought might be involved in painful periods.¹² By 1965 his group was measuring prostaglandins in endometrium and menstrual fluid from people with and without dysmenorrhea.¹³ Looking back in 1979, Pickles described how endometrial prostaglandins stimulate the contractions of the uterus at menstruation, and how excessive action of this kind produces dysmenorrhea.¹⁴

It is sometimes said that menotoxin turned out to be prostaglandin. A 2025 systematic review puts it that way, writing that the menotoxin was “later revealed to be prostaglandin.”¹⁵ That is a simplification. In the same 1979 survey, Pickles still treated “menotoxin” as a separate question: in the abstract’s words, “an unidentified substance which is toxic to certain plants and which may or may not prove relevant to gynecology.”¹⁴ Prostaglandins explain cramping within the body of the person menstruating. They do not explain wilting flowers, spoiled meat or failed bread dough, and no one has shown that those effects exist.

Current understanding

Today menstruation is understood as the shedding of the upper, functional layer of the uterine lining when progesterone falls at the end of a cycle without pregnancy. It occurs in only a small minority of animals, humans among them. “Menstruating endometrium is rich in cytokines and prostaglandins,” a 2020 review notes, and researchers now study menstrual effluent for what it can reveal about conditions such as endometriosis.¹⁶ The 2025 review found that eight studies reported higher prostaglandin levels in the menstrual effluent of people with painful periods and that anti-inflammatory drugs (NSAIDs) lowered them. It also found that the studies were small and that other molecules may matter as well.¹⁵ An Austrian science supplement put the basic point plainly in 2013: menstrual blood consists of uterine lining and blood.²

The same 2020 review notes that stigma around menstruation remains a barrier to diagnosis, to people seeking care, and to research. It also shows how little attention menstrual blood itself received: a PubMed search for the term found one publication from 1941 to 1950, against more than 400 in the decade before the review.¹⁶ The menotoxin years are part of that story. For three decades, some of the attention that medicine did give to menstrual fluid went into a search for a poison, designed to confirm a belief. Scientists who reported negative results were sometimes treated as exceptions to be explained away. Hegg’s thesis goes further and argues that the waves of menotoxin research coincided with periods of advance for the women’s movement. That interpretation is hers, but the timing she describes, the 1920s and the 1970s, matches the publication record above.¹⁰

The useful lesson is not that early twentieth-century researchers were uniquely credulous. Many of them ran comparisons with controls, and their own data often contained the answer. Freeman’s 22 women and the men’s sweat in Gengenbach’s tests showed no special menstrual effect. What failed was the readiness to let a negative result count.

Footnotes

1. Pliny, Natural History 7.13 (Bostock and Riley), Perseus. ↩

2. S. Burger, Falter Heureka 1/2013. ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Clancy, Scientific American blog, September 9, 2011. ↩ ↩² ↩³

4. Gengenbach 1925, pp. 5-19. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

5. Ashley-Montagu 1940, pp. 211-218. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

6. Macht and Lubin 1923 (Crossref record). ↩

7. Freeman, Looney and Small 1934 (Crossref record). ↩

8. Zondek 1953 (Crossref record). ↩

9. Skepchick, September 2, 2021, summarizing Zondek 1953. ↩

10. Hegg 2024, thesis abstract. ↩ ↩²

11. Ernster 1974; Bryant, Heathcote and Pickles 1977 (bibliographic records). ↩

12. Pickles 1960, abstract. ↩

13. Pickles et al. 1965 (bibliographic record). ↩

14. Pickles 1979, abstract. ↩ ↩²

15. Kyathanahalli et al. 2025, abstract and introduction. ↩ ↩²

16. Critchley et al. 2020, sections I, IV and on menstrual health research. ↩ ↩²