How Does Cyra Track Hormones? Your Most Common Questions Answered

Since announcing Cyra, we have received thousands of questions about how continuous hormone monitoring actually works. We have collected the most common ones and answered them as directly and honestly as we can.

Does Cyra Measure Hormones Directly Through the Skin?

No. Noninvasive, transdermal hormone measurement (measuring hormones directly through the skin without breaking it) remains a significant technical challenge. The concentrations are low, the skin is an imperfect optical medium, and the signals are difficult to isolate from noise.

What Cyra measures is a set of physiological signals that correlate with hormonal state: heart rate variability, skin temperature, skin impedance, movement patterns, and sleep architecture. These signals, processed together by a machine learning model trained on paired sensor-and-blood-test data, produce estimates of hormonal state.

Think of it less like a glucose monitor (which does measure glucose directly through the skin) and more like a sophisticated inference engine that reads the body's responses to its own hormones.

How Accurate Is Continuous Hormone Tracking Compared to a Blood Test?

Accuracy is the right question to ask, and we want to answer it precisely rather than reassuringly.

For cycle phase detection (identifying whether you are in the follicular phase, approaching ovulation, or in the luteal phase), our internal validation shows accuracy comparable to commercial ovulation predictor kits, with the significant advantage of providing continuous rather than episodic information.

For ovulation prediction specifically, we can identify the approach of ovulation an average of 3 to 5 days in advance, with accuracy rates that improve significantly after the system has had 2 to 3 cycles to learn your individual patterns.

For hormone level estimation, including your actual estradiol or progesterone numbers, we are not attempting to replace laboratory testing. Our estimates are calibrated to be directionally accurate, but they are not laboratory measurements and should not be used as substitutes for clinical blood testing.

Why Does Cyra Take a Few Cycles to Reach Full Accuracy?

Your physiology is individual. The model starts with general patterns learned from our training data, but your specific baseline (your typical temperature trajectory, your usual heart rate variability patterns, and the particular shape of your cycle) is unique to you.

Over the first 2 to 3 cycles, the model is learning your individual baseline. It is figuring out what "normal" looks like for you specifically, so that it can detect meaningful deviations. This is why accuracy improves over time: the model is becoming personalized.

Can Cyra Detect Hormonal Disorders Like PCOS or Endometriosis?

No. Cyra is not a medical device and does not diagnose conditions. It does not detect PCOS, endometriosis, premature ovarian insufficiency, or any other hormonal disorder.

What it can do is surface patterns in your data that you might want to discuss with a clinician. Cycles that are consistently longer or shorter than typical, patterns that suggest irregular or absent ovulation, unusual temperature trajectories. These are things the app can flag as potentially worth discussing with your doctor.

We are careful about this because the line between "surfacing patterns" and "diagnosing conditions" matters enormously, both for safety and for regulatory reasons.

How Do Stress, Illness, and Travel Affect Hormone Tracking Accuracy?

Physiological stressors affect the signals Cyra measures. A fever will change your skin temperature in ways that don't reflect hormonal state. High stress alters heart rate variability. Jet lag disrupts sleep architecture.

The model is designed to handle typical variation, but significant stressors will affect accuracy. The app will flag periods where the data quality is lower, and results during those periods should be interpreted with appropriate caution.

What Health Data Does Cyra Collect and Where Does It Go?

This is the question we think matters most, and we have designed our answer to it carefully.

Your raw biometric data (the signals from the sensors) never leaves your phone. All processing happens locally. The AI model runs on your device.

We collect anonymized, aggregated data for model improvement purposes, but only with explicit opt-in consent, and only in a form where it cannot be linked back to you. Your personal health history is yours.

The longer answer is in our privacy architecture article, which explains in detail why "we cannot access your data" is an architectural fact rather than a policy promise.

When Will Cyra Be Available to Download?

We are currently in the final stages of development and targeting a launch later this year for Founding Members. The app will be available on iOS and Android.

If you are interested in early access, the waitlist is open. Founding Members receive priority access, 20% off their annual subscription, six months of Cyra Pro free, and a fully refundable reservation until launch.

We will share more specific timelines as we get closer to launch.