From endometriosis and cervical cancer, to diabetes, vitamin D deficiency and pollution exposure, scientists are finding period blood offers a window into women's wellbeing.
Like many women who menstruate, Emma Backlund prefered not to think too much about the blood she shed every month. But when biotech startup NextGen Jane asked for her period blood in 2023, Backlund readily saved eight tampons from one menstrual cycle and popped them off in the post to the firm's laboratory in Oakland, California.
Sure, it was an unusual request, but a relatively fuss-free one she was more than happy to help with – especially if it meant future girls avoiding the painful ordeal she faced growing up.
"When I turned 11, I got my first period and I thought I was dying," says Backlund, a 27-year-old graduate student from Minnesota, in the US. "I remember telling my mum that I needed to go to the hospital. And pretty much every period I've had since then was like that. I would throw up every month. I missed out on social activities and school. It was just this burning, stabbing, gut-wrenching pain that continued."
A medical gold mine
Urine samples have been examined by physicians since Babylonian and Sumerian times, some 6000 years ago. Stools and venous blood followed suit one and two centuries ago. But period blood hasn't ever received much clinical attention. Yet, it is a complex fluid: half of it is regular blood, while the remainder comprises proteins, hormones, bacteria, endometrial tissue and cells sloughed off from the vaginal cavity, cervix, fallopian tubes, ovaries, and more.
"You get access to cell types and other molecular signatures that you just don't get from whole blood, saliva, and other sample types," says Tariyal. "It's essentially a natural biopsy that's providing you insight into the reproductive organs." Her firm, NextGen Jane, sends out specially designed cotton tampons to volunteers like Backlund and has analysed more than 2,000 menstrual samples from more than 330 women since its founding in 2014.
"You can use [menstrual blood] to look for any conditions that affect the uterus – and there are many," says Christine Metz, a reproductive biologist with the Feinstein Institutes for Medical Research at Northwell Health, in the US.
Metz started out studying menstrual blood to pinpoint endometriosis biomarkers more than a decade ago, but is now also keen to see if the body fluid might provide clues to other conditions, such as endometrial cancer, adenomyosis, which is when the uterus lining grows into the uterine wall, and endometritis, which is persistent inflammation of the endometrial lining.
"Menstrual effluent has a lot of value for understanding uterine health, which we don't have ways of accessing otherwise," says Metz. "It's a very unique biological specimen." One study, for instance, identified 385 proteins found exclusively in mensural blood.
