Period‑tracker apps share women's health data with tech firms

The Mozilla Foundation examined the privacy practices of six popular menstrual‑cycle tracking apps – Stardust, Flo, Clue, Spot On, Period Calendar and Euki. The study found that Stardust, which combines cycle tracking with astrology, transmits detailed reproductive‑health information – including pregnancy status, birth‑control method, mood, alcohol consumption and specific symptoms – to the analytics service RudderStack, a company not mentioned in its privacy notice. All the other apps were shown to send at least basic user identifiers to advertising platforms operated by Google, Meta, Microsoft and TikTok.

Euki received the highest privacy rating, sharing virtually no data with third parties. Researchers warned that, after the U.S. Supreme Court’s 2022 decision overturning federal abortion protections, health data from such apps could be subpoenaed for criminal cases, raising concerns about privacy and security for millions of women worldwide.