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What is the cortisol awakening response?

Last updated: October 15, 2026

The cortisol awakening response (CAR) is a 50 to 75 percent rise in cortisol, usually measured in saliva, in the first 30 to 45 minutes after waking. It is a normal part of the daily cortisol rhythm and is thought to help prepare the body for the day ahead.

The pattern in detail

Cortisol does not jump at wake-up from a flat baseline. The hormone already rises during the second half of the night. Then, after waking, the rise sharpens: cortisol climbs over the next 30 to 45 minutes (Stalder et al., 2016), reaches its highest level of the day, then declines gradually until evening.

The "awakening response" specifically refers to the post-wake rise, not the slower pre-wake increase. In studies that sampled saliva from the moment of waking, free cortisol rose by 50 to 75 percent within 30 minutes (Pruessner et al., 1997). Pooling four studies of 509 adults, Wüst et al. (2000) found an average rise of about 50 percent, with roughly 1 in 4 people showing no clear rise.

What CAR may do

Its exact function is still debated (Fries et al., 2009). What is known about cortisol in general, and about the CAR in particular:

• Mobilizes glucose. Cortisol helps the liver produce glucose, raising the fuel available to the body and brain.
• Prepares for the day. The leading hypothesis is that the CAR reflects anticipation of the day ahead (Fries et al., 2009).
• Calms inflammation. Cortisol is an anti-inflammatory hormone.
• May help you wake up. Clow et al. (2010) discuss a possible link between the CAR and the end of sleep inertia; it has not been proven.

The CAR is not a reaction to a threat: in most healthy people it happens every morning, as part of the normal daily cortisol rhythm (Clow et al., 2010).

What controls the response

Three main factors:

1. The body clock. The brain's master clock (the suprachiasmatic nucleus) is involved in regulating the CAR, along with the hippocampus and other regions (Fries et al., 2009; Clow et al., 2010).
2. Light exposure. Light after waking amplifies the response: in a lab study, 800 lux of light raised morning cortisol about 35 percent more than darkness (Scheer & Buijs, 1999).
3. Anticipation and stress. A larger rise has been linked with job stress and general life stress (Chida & Steptoe, 2009).

Why this matters for waking up

The CAR and the fading of sleep inertia happen in the same window, and some researchers have proposed a link between them (Clow et al., 2010). But it has not been shown that changing your CAR changes how groggy you feel. Two findings worth knowing:

• Light after waking boosts it. Opening the curtains or stepping outside is the simplest way to get that light (Scheer & Buijs, 1999).
• Snoozing did not clearly change it. In a 2024 lab study, 30 minutes of snoozing had no clear effect on the CAR (Sundelin et al., 2024).

Wüst et al. (2000) also found that the time of waking, sleep duration and even whether people used an alarm clock had no considerable impact on the CAR. The popular claim that coffee right after waking "blunts" the CAR is not backed by the studies cited here.

Disruption signals (what CAR can tell you about your health)

In a meta-analysis of 147 studies, a larger rise after waking was linked with job stress and general life stress, and a smaller rise with fatigue, burnout or exhaustion (Chida & Steptoe, 2009). Findings vary between studies, and there are no agreed cut-offs for a "blunted" or "exaggerated" CAR.

CAR is a research marker, not a clinical test. Measuring it properly requires timed saliva samples starting at the exact moment of waking (Stalder et al., 2016), so there is no reliable consumer way to check your own. If you feel groggy for an hour or more most mornings despite enough sleep, talk to a doctor.

How to support a healthy morning

1. Anchor your wake time. Even on weekends, as the CDC recommends for sleep in general.
2. Get light soon after waking. Sunrise, a light therapy lamp, or open curtains.
3. Get up and move. It makes going back to sleep much harder.
4. Give yourself a task right away. A mission alarm does this for you, so you are not tempted to lie back down.

These overlap with the sleep inertia tips.

Sources

1. Fries, Dettenborn & Kirschbaum, International Journal of Psychophysiology, 2009. The cortisol awakening response (CAR): facts and future directions
2. Pruessner et al., Life Sciences, 1997. Free cortisol levels after awakening: a reliable biological marker for the assessment of adrenocortical activity
3. Wüst et al., Noise & Health, 2000. The cortisol awakening response: normal values and confounds
4. Stalder et al., Psychoneuroendocrinology, 2016. Assessment of the cortisol awakening response: Expert consensus guidelines
5. Clow et al., Neuroscience & Biobehavioral Reviews, 2010. The cortisol awakening response: more than a measure of HPA axis function
6. Scheer & Buijs, Journal of Clinical Endocrinology & Metabolism, 1999. Light affects morning salivary cortisol in humans
7. Chida & Steptoe, Biological Psychology, 2009. Cortisol awakening response and psychosocial factors: a systematic review and meta-analysis
8. Sundelin et al., Journal of Sleep Research, 2024. Is snoozing losing? Why intermittent morning alarms are used and how they affect sleep, cognition, cortisol, and mood
9. Centers for Disease Control and Prevention. CDC — Sleep and Sleep Disorders