'It's a very unique biological specimen': What menstrual blood can reveal about your health

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." It took Backlund 13 years to discover she had endometriosis, a chronic, debilitating di