SF startup Muse Bio is recruiting menstrual blood donors with $40 payments to build a biobank of menstrual‑derived stem cells (MenSCs) for cosmetics, regenerative medicine and fertility applications. The company argues menstrual fluid is a noninvasive, rich source of multipotent stem cells and plans phased commercialization starting with skin‑care products and eventual clinical programs. The approach raises ethical and regulatory questions about donor compensation and downstream clinical use, while academic initiatives—such as MIT’s menstruation science efforts—signal growing scientific interest in the tissue.