Abhishek Mahajan (narrator / author)

But there is some decent evidence for it being at least partially explanatory.

A strong piece of proof for it is that women with obstructive malarian anomalies or uterine deformations that can lead to more retrograde menstruation have a higher risk of endometriosis compared to women with no abnormalities.

But despite how often the theory is repeated amongst doctors, it cannot explain all endometriosis cases.

Why not?

For one, retrograde menstruation occurs in between 75-90% of women, most of whom never go on to develop endometriosis.

Keep in mind that obstructive malarian anomalies occur in 1-5% of the population, and endometriosis rates are about 10% of the population.

and endometriosis itself is almost certainly underdiagnosed.

We'll discuss the insanity of this 10% number later, but, suffice to say, while retrograde menstruation may play some role in the development of the disease, it cannot cover the full scope of cases.

To be fair, malaria anomalies are also underdiagnosed, but it feels unlikely to make up the gap.

2.

Endometriosis comes in multiple forms, some of which stay localized to the pelvic region, yes, but endometriosis can occur in absurdly distal regions as well.

Where else?

Literally everywhere.

Type an organ system plus endometriosis into Google and you'll find at least one case report of it happening there.

the gastrointestinal tract, the lungs, and, insanely enough, the brain as well.

How could backwards flow of uterine blood explain that?

And three, perhaps most damning of all, is that endometriosis has been found in people who have never menstruated at all.

Such as premenarchal girls between the ages of the 8th of May, 13, women who genetically lack a uterus, and even cisgender men.

This last bit is a particularly rare phenomenon, with only 16 cases reported in the literature circa 2018, but it conclusively exists.

One interesting note.