Cortisol is the body’s primary steroid hormone, produced by the adrenal glands in response to stress. It manages the body’s response to physical and psychological challenges. Measuring cortisol levels provides insight into the function of the stress-response system. Assessing the hormone in saliva is a valuable, non-invasive method for monitoring daily and long-term patterns, offering a unique window into the biologically active portion of the hormone circulating throughout the body.
The Hormonal Role of Cortisol
Cortisol is a glucocorticoid synthesized from cholesterol in the adrenal cortex. Its purpose is to mobilize the body’s resources to cope with a perceived threat, often termed the “fight-or-flight” response. This process involves the Hypothalamic-Pituitary-Adrenal (HPA) axis, a complex network of communication that begins in the brain when a stressor is encountered.
The hypothalamus releases corticotropin-releasing hormone (CRH), signaling the pituitary gland to release adrenocorticotropic hormone (ACTH. ACTH travels to the adrenal glands, stimulating them to synthesize and secrete cortisol. This release helps restore balance in the body following a stressful event.
The hormone primarily focuses on energy regulation. Cortisol promotes gluconeogenesis—the creation of new glucose from non-carbohydrate sources—ensuring the brain and muscles have immediate fuel. It also influences the immune system by suppressing inflammation and modulating immune cell activity. While this temporary shift is designed for short-term survival, chronic activation can lead to long-term systemic effects.
Why Saliva Testing Is Used
Saliva testing focuses on the active hormone, offering an advantage over traditional blood or urine measurements. In the bloodstream, 90% or more of cortisol is bound to carrier proteins, such as Cortisol-Binding Globulin (CBG), making it temporarily inactive and unable to interact with cell receptors.
Saliva contains only the unbound, or “free,” fraction of cortisol, which is biologically active and affects tissues. Measuring this free cortisol provides a more accurate reflection of the hormone’s availability at the cellular level. This is important because conditions altering blood protein levels, such as liver or kidney diseases, can skew total cortisol measurements in blood tests.
The collection process is simple, non-invasive, and stress-free, helping ensure accurate results. Patients can collect samples at home multiple times daily using passive drool or a cotton swab. This avoids the stress-induced cortisol spike caused by a clinic visit or venipuncture, allowing for the mapping of full-day cortisol patterns necessary for proper interpretation.
Understanding the Diurnal Rhythm
Salivary testing primarily charts the diurnal rhythm, the body’s natural 24-hour cycle of cortisol fluctuation. In a healthy individual, cortisol levels peak shortly after waking and reach their lowest point late at night before sleep. This cycle reflects the HPA axis aligning with the body’s internal clock.
The Cortisol Awakening Response (CAR) is a sharp increase in cortisol occurring within 30 to 45 minutes of waking. This surge typically results in a 50% to 75% rise in levels and prepares the body for the day’s physical and mental demands. Monitoring the CAR is a key indicator of the HPA axis’s dynamic response capability.
Deviations from this pattern are often more informative than a single reading. A “flat” curve, where levels remain stable without a morning peak or evening decline, is associated with chronic stress or fatigue. Consistently elevated evening cortisol, where the hormone fails to drop to its nightly nadir, interferes with sleep and signals perpetual alertness. A blunted or absent CAR may suggest a depleted stress response system, while an exaggerated CAR can indicate chronic worry or acute stress.
Lifestyle Factors That Affect Levels
Salivary cortisol measurements are sensitive to daily behaviors and environmental factors, which must be considered during interpretation. Physical activity is a strong modifier; intense or prolonged exercise can acutely elevate cortisol concentrations by as much as 80% immediately afterward. Testing protocols require avoiding strenuous exercise before collection.
Food intake also temporarily influences the hormone, with levels increasing about 10% an hour after a meal. This temporary spike highlights cortisol’s role in managing energy and metabolism. The mode of awakening impacts the CAR; waking naturally often results in a smaller CAR compared to being abruptly woken by an alarm clock.
Other factors temporarily alter measurements. Acute emotional stress, such as preparing for a difficult presentation, causes a significant, short-term rise. While the influence of moderate consumption of coffee, alcohol, or nicotine on overall daily cortisol levels is often minor, the timing relative to sample collection remains important. Understanding these temporary influences is necessary to distinguish between a short-term reaction and a long-term pattern of HPA axis function.