In 1920, Hungarian physician Béla Schick ran a highly questionable experiment.
He asked several women, some on their periods, to briefly hold flowers.
Then, without proper controls and relying solely on his own observations, he claimed that the blooms held by the menstruating women wilted more quickly.
Schick's explanation for this was not only unscientific, but also played into age-old myths about periods.
He concluded that menstruating women's bodies release toxins, excreted in sweat and blood, that can kill plants.
While it unfortunately took decades to debunk Schick's so-called menstrual toxin hypothesis, some good did come from this work.
The idea prompted investigations into the composition of menstrual fluid, eventually leading to a discovery that helped explain a very real problem period cramps.
Anywhere from 50 to 90 of people who menstruate deal with painful abdominal or pelvic cramps during their period, a condition known as dysmenorrhea.
Individual experiences can vary from mild discomfort to throbbing aches, to contraction-like cramps that rival the pain of labor.
Cramping can extend into the back and thighs and be accompanied by bloating, nausea and even vomiting.
And for at least 10 of people who menstruate, these symptoms are so severe that they disrupt their day-to-day activities.
Healthcare experts classify dysmenorrhea into two main types, primary and secondary dysmenorrhea.
For some, menstrual cramps can be traced back to underlying conditions, including endometriosis, where tissue similar to the uterine lining grows outside the uterus, or uterine fibroids, which are non-cancerous growths.
This type of pain is called secondary dysmenorrhea.
While these cases can be linked to specific conditions, the origins of pain are often not well understood.
For example, endometriosis can lead to scarring and inflammation, and uterine fibroids can push against other organs, both of which can cause discomfort.
Yet the intensity of cramp pain doesn't always match the severity of these factors.
And because the conditions are so variable, so is the treatment.
Primary dysmenorrhea, on the other hand, is much more common, and it refers to painful menstrual cramps that can't be linked to an underlying condition.
Despite how misguided Schick's experiments were, they set a path toward better understanding this pain.
While early researchers obviously never found a menstrual toxin, in the 1960s and 70s scientists studying menstrual fluid did discover the presence of compounds called prostaglandins.
And further research showed that many people with painful period cramps often had higher levels of prostaglandins in their menstrual fluid.
One important role of prostaglandins is to stimulate the muscles of the uterus to contract, an essential step in shedding the uterine lining during a period.
So it's thought that an excess of prostaglandins may intensify these contractions, causing pain.
This process can also cause blood vessels to constrict, reducing the flow of oxygen and releasing chemicals that activate pain receptors.
Since many over-the-counter pain medications like naproxen and ibuprofen work by targeting prostaglandins, they can provide relief for some people with period pain.
Others find hormone-based contraceptives that thin the uterine lining and, in turn, reduce prostaglandin production to be helpful.
But while prostaglandin research was foundational and shaped the way we understand menstrual pain, in recent years it's become evident that prostaglandins are just part of the story.
Many other factors likely contribute to painful cramping, including hormones inflammation, brain pathways and perhaps even the microbiome.
And because period pain is not fully understood, existing treatments don't always work for everyone.
On top of that, talking about menstrual cramps can feel awkward or even taboo, leading many people to feel that they have to simply put up with the pain.
But regularly suffering from severe cramping is far from benign.
Some experts believe that repeated exposure to pain can cause the nervous system to become more sensitive, leaving a person vulnerable to developing chronic pain conditions.
That's why more research is needed to untangle the complex drivers of this surprisingly common experience and to develop better treatments.
That work can start with recognizing that period.
Pain is real and it affects hundreds of millions of people.
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