The Cortisol Awakening Response: Why Mornings Feel Different

If you have ever noticed that you feel most alert, or most keyed up, in the first hour after waking, there is real physiology behind that. Cortisol follows a daily rhythm that reaches its highest point not in the middle of a stressful afternoon, but shortly after you open your eyes. Researchers call this specific spike the cortisol awakening response, or CAR: a rise in cortisol of roughly 50 to 75 percent above overnight lows, occurring in the first 30 to 45 minutes after waking, distinct from the slower decline cortisol follows for the rest of the day.

The proposed function is preparatory. Endocrine Reviews describes the CAR as a burst thought to help the body ready itself for the demands of the day ahead, mobilizing glucose and priming attention and energy systems before you have even gotten out of bed. It is a separate mechanism from the general daily cortisol curve, which also peaks around this same window and then gradually tapers toward its lowest point around midnight; the CAR is layered on top of that curve specifically at the moment of waking.

What is less settled is exactly why the CAR happens, and even whether waking itself is the trigger. A 2025 study in Proceedings of the Royal Society B used continuous in vivo microdialysis in 201 healthy volunteers and found that the rate of cortisol secretion did not measurably change at the moment of waking compared with the hour before, challenging the long-held assumption that the act of waking itself accelerates cortisol release. The same research found considerable variability between individuals, partly explained by how long someone had slept and what time they woke up relative to the previous day, suggesting the CAR may be less a fixed alarm-clock reflex and more a product of someone's broader sleep pattern.

Other recent research has focused on what predicts a larger or smaller CAR on a given morning. A 2024 pilot study in Biological Psychology found that anticipating a stressful day was associated with a measurably larger cortisol rise after waking, suggesting the CAR responds to psychological expectation and not just biological clock time. Separate 2025 research has linked variability in the CAR to sleep efficiency, and to differences in trait anxiety and psychological resilience, though researchers still describe the relationship between CAR size and mental health outcomes as inconsistent rather than settled.

This is where the science and the wellness-marketing version of cortisol diverge. The CAR has been proposed as a biomarker for HPA axis function, and researchers do use it in studies of stress and stress-related conditions. But that is a long way from the claim, common in supplement and skincare marketing, that a "bad" morning cortisol spike can be identified and corrected with a specific product. The research at this point supports the CAR as a real, measurable, and still only partly understood physiological event, not a dial with a known correct setting.

What is genuinely actionable is more mundane than any product claim: sleep duration and consistency appear repeatedly across this research as one of the clearer influences on cortisol awakening patterns. That lines up with general sleep-hygiene guidance rather than pointing to a novel intervention, and it is a good example of a broader pattern on this site, where the well-supported version of a cortisol claim usually turns out to be less exciting, and more about basic habits, than the version that goes viral.