Your body's stress hormone has a healthy daily rhythm — the problem starts when the stress response never switches off.
Cortisol gets a bad reputation online as "the stress hormone" to be avoided entirely — the reality is more nuanced, and more interesting.
Cortisol follows a healthy daily rhythm, typically peaking shortly after waking to help you feel alert, and gradually declining through the day. This daily curve is a normal, useful part of your physiology, not a sign of stress in itself.
The issue arises when stress is chronic rather than occasional — when the body's stress response stays activated for weeks or months rather than resolving after the stressful event passes. Sustained elevated cortisol has been associated with disrupted sleep, changes in appetite and blood sugar regulation, and altered immune signalling that can contribute to chronic inflammation.
Chronic stress often doesn't feel like acute panic — it can feel more like low-grade fatigue, irritability, or just "being busy for a long time." That subtlety is exactly why THE FAD's Stress signal asks about several indirect markers (sleep, mood, social connection) rather than asking you to simply rate "how stressed am I," which people often answer inaccurately for exactly this reason.
This is general physiology education, not a diagnosis. If you suspect a stress-related health issue, a doctor can evaluate this properly — self-tracking is a complement to that, not a substitute.