Menstruation apps used to track your cycle, sex life and moods are using that private information to give Facebook insights about their users — even if they don’t have Facebook accounts, a new report found.

Privacy International, a UK-based advocacy group, found that period trackers Maya and MIA Fem have shared user information with the social media giant for the purpose of better ad targeting.

“Our traffic analysis reveals … that Maya informs Facebook when you open the app,” Privacy International reported. “There is already a lot of information Facebook can assume from that simple notification: that you are probably a woman, probably menstruating, possibly trying to have (or trying to avoid having) a baby. Moreover, even though you are asked to agree to their privacy policy, Maya starts sharing data with Facebook before you get to agree to anything.”

The way Facebook can access this information is through a tool called the Facebook Software Development Kit (SDK). App developers use the tool to improve their apps, understand user preferences and to allow their users to log into the app via Facebook. Similarly, Facebook will take the information provided by app developers to target individuals with personalized ads.

If you search through Maya’s terms and privacy policy, you’ll find that the app stores private information that includes: any personal notes, symptoms, length of menstruation cycle, physical intimacy, planned pregnancy and your mood.

That information can be especially helpful to advertisers. For example, jotting down your daily mood can allow them to strategize on what they might sell you.

“Knowing when a teenager is feeling low means an advertiser might try and sell them a food supplement that is supposed to make them feel strong and focused. Understanding peoples' mood is an entry point for manipulating them.”

According to section 4.4 of their privacy policy, Maya states that they don’t share identifiable user information with advertisers; however, they do occasionally share user information that’s been made anonymous to help advertisers reach their target audience.

“We use third-party advertising companies to serve advertisements when You visit our Platforms. These companies may use information (not including your name, address, email address, or telephone number) about Your visits to this and other platforms in order to provide advertisements about services of interest to You,” as stated in section 7.0 of Maya’s privacy policy.

Reps for Maya by Plackal Tech, which has more than 5 million downloads on Google Play, told Privacy International that they have since stopped using Facebook core SDK and Analytics SDK on their app, but they will continue to use Facebook ad SDK. Their latest version of the app will show the change on Google Play Store and those changes are expected to show in the Apple App Store this weekend.

“Maya does not share any personally identifiable data or medical data with the Facebook Ad SDK,” Maya told Privacy International. “The Ad SDK helps us earn revenue by displaying ads that our users can opt out of by subscribing to Maya's premium subscription.”

MIA Fem chose not to have their response published in the report.

This isn’t the first time a period tracker app has shared user data with Facebook.

In February, The Wall Street Journal found that Flo Period & Ovulation Tracker by Flo Health Inc. told Facebook each time a user menstruated and when a user was planning a pregnancy. According to the report, the app didn’t offer its users a clear way to opt out of sharing their information.

Facebook notified Flo, as well as other apps found in the Wall Street Journal’s report, to stop releasing sensitive information to them. Flo has since promised to make changes on its platform.

“Facebook said some of the data sharing uncovered by the Journal’s testing appeared to violate its business terms, which instruct app developers not to send … ‘health, financial information or other categories of sensitive information,’” The Wall Street Journal reported.

Susana Guerrero is an SFGATE digital reporter. Email: [email protected] | Twitter: @SusyGuerrero3