The world of tracking apps has grown in the last decade, but where does all that data go? India speaks to the Chief Medical Officer of Clue, Dr Lynae Brayboy about the importance of tracking periods, and the link between tracking apps and research. Later, India is joined by Eva Blum-Dumontet, a Senior Policy Advisor on Artificial Intelligence at Royal Society who formerly carried out key research into data and tracking apps. Eva offers a word of warning over the type of data these apps ask for. Credits: Presented by India Rakusen. Producer: Ellie Sans. Assistant Producer:Jorja McAndrew. Executive Producer: Suzy Grant. Original music composed and performed by Rebekah Reid. Sound design by Olga Reed. Special thanks to all contributors and audio diarists. A Listen production for BBC Radio 4 and BBC Sounds.