BMJ Analysis: Cycle-Tracking Apps Pose Substantial Health and Privacy Risks

A new analysis in The BMJ argues that digital menstrual cycle trackers and "cycle syncing" lack scientific evidence. Apps estimate ovulation from self-reported bleeding without measuring hormones and may share data with third parties.

• About 50 million people worldwide use menstrual cycle-tracking apps
• Sports science shows no generalizable link between cycle phases and performance
• Many apps lack transparency reports and easy data deletion
• Risks are higher where abortion is criminalized