Information about your mood, sex life, and (if you're a woman) menstrual cycle is highly personal stuff; it's also super valuable to advertisers. And according to a new report, if you use certain period-tracking apps, you could be sending that intimate information directly to Facebook.

First, some good news. A report from Privacy International, published Monday in conjunction with BuzzFeed News, found that the five most popular period-tracking apps have taken proactive measures to protect your data. Namely, they don't share information about your body and mental health with Facebook and its vast advertising network.

The not so great news? There are period-tracking apps out there with millions of downloads that integrate Facebook's Software Developer Kit (SDK) and give your most personal information to Facebook, its ad network, and third-party analytics companies.

The data these apps share goes beyond the dates and times of your period. It also includes information like whether you're having unprotected sex, when you're feeling sad or vulnerable, what kind of medications you're taking, whether you're trying to get pregnant, and more. All of this is valuable to advertisers. Notably, gaining information about mood and mental health — aka "psychographic targeting" — has been exposed in the past (remember Cambridge Analytica) as a powerful advertising targeting tool to reach people in the right frame of mind to be swayed.

Privacy International previously surveyed some of the most popular apps overall and found that 61 percent shared personal information with Facebook for ad targeting. At the time, that included the period-tracking app Clue, which reformed its data practices in response. (Flo has also since changed its data policies.)

The apps that received the organization's "all clear" are Period Tracker by Leap Fitness Group; Period Tracker Flo by Flo Health, Inc.; Period Tracker by Simple Design Ltd.; and, as previously mentioned, Clue Period Tracker by Biowink.

The apps causing the biggest concern were Maya by Plackal Tech and MIA by Mobapp Development Limited. Maya, based in India, has 5 million downloads on Google Play, and MIA, based in Cyprus, has 1 million (and boasts 2 million users). Other apps that reportedly share sensitive data are My Period Tracker by Linchpin Health, Ovulation Calculator by Pinkbird, and Mi Calendario by Grupo Familia.

Though it's a period-tracking app, Maya prompts users to enter lots of information relating to their physical, sexual, and mental health. That includes the date and time of your period, physical symptoms (like nausea), your mental state (like sad or vulnerable), dates, times, and contraception details of your sexual encounters, and even personal diary entries. This is shared with Facebook for ad targeting, as well as a third-party "customer retention" company.

Maya informed Privacy International that it would reduce its integration with Facebook's SDK. It said it'll still use the Facebook ad network on its own site, after users consent, but will share less data overall.

The second popular company, MIA, was not as responsive as Maya. It declined to respond to the organization after it learned that BuzzFeed would be covering the report, and got hostile with BuzzFeed in the days leading up to publication.

It also includes information like whether you're having unprotected sex ...

MIA engages in many of the same practices as Maya, with the addition of targeting articles to you based on your lifestyle behaviors like masturbation and alcohol consumption. When you click on an article, it sends that information to Facebook and a third-party analytics company.

Privacy International found that the five apps it was most concerned about tell Facebook when you're opening the app — revealing that you're opening a period app in the first place, as well some personal information, like gender, before you even agree to the terms of service.

Of course, it's not just period-tracking apps collecting your data. Health tech is a booming industry. And that means more people are turning to digital tools to help manage their most intimate issues — while possibly exposing themselves to advertisers in the process.

UPDATE: Sept. 10, 2019, 3:30 p.m. PDT

Facebook requested that Mashable include the following statement from a spokesperson. It emphasizes that Facebook's terms of service do not permit sharing "sensitive health data" (Facebook told Buzzfeed it is looking into the apps). It also contends that Facebook does not look at off-Facebook activity for interest-based ad-targeting (Facebook does look at off-platform activity for other types of ad targeting).