Cortisol is a steroid hormone produced by the adrenal cortex and classified as a glucocorticoid. It acts through intracellular receptors to influence glucose metabolism, immune activity, blood pressure, and brain arousal, and is a central component of the body’s stress-response system. Identified and characterized in the early 20th century, cortisol became a key marker for studying stress biology and circadian regulation. One clinically useful feature is the Cortisol Awakening Response (CAR): a rapid increase in cortisol levels within the first 30–45 minutes after waking. This morning peak links signals from the brain’s circadian pacemaker, sleep-wake timing, and adrenal output, helping coordinate morning alertness, energy mobilization, and downstream hormone interactions across the day.

Higher waking cortisol levels may reflect increased HPA-axis activation or a pronounced morning stress response. Common associations include recent or anticipatory stress, poor or short sleep, shift work or circadian misalignment, stimulant or nicotine use, and systemic inflammatory signals. Elevated waking cortisol can also appear when the whole diurnal rhythm is shifted earlier. Lower waking cortisol levels can indicate a blunted Cortisol Awakening Response or reduced morning adrenal activation. This pattern may be associated with prior prolonged stress exposure, disrupted sleep timing, recovery states after extended stress, certain medications, or altered circadian signaling. Interpretation is most reliable when combined with other saliva timepoints, urinary cortisol metabolites, DHEA, and clinical context rather than from a single sample alone.

Included in the Hormone Zoomer to map the morning component of cortisol rhythm, Saliva Cortisol – Waking evaluates timing and strength of the Cortisol Awakening Response. When paired with midday/evening saliva samples and urinary hormone metabolites, it helps distinguish altered timing from changes in overall adrenal output, informing more precise assessment of stress rhythms and metabolic signaling.