Cortisol is a hormone found primarily in your blood, though it also passes into your saliva, urine, and even your hair. Produced by the adrenal glands that sit on top of your kidneys, cortisol plays a central role in how your body manages energy, responds to stress, and controls inflammation. Understanding where cortisol shows up in the body matters because each location tells a different story about your health, and doctors choose which one to measure based on what they’re looking for.
Where Cortisol Is Produced
Cortisol is made in a specific layer of your adrenal glands called the zona fasciculata. You have two adrenal glands, one perched on top of each kidney, and each one has an outer shell (the cortex) and an inner core. The outer cortex has three distinct zones, and the middle zone is the one dedicated to cortisol production. Your brain controls how much cortisol gets released through a signaling chain: the hypothalamus signals the pituitary gland, which then tells the adrenal glands to ramp production up or down based on what your body needs at any given moment.
Cortisol in Your Blood
Most of your cortisol circulates in your bloodstream, which is why a blood draw is the most common way to measure it. Normal morning levels typically fall between 5 and 25 mcg/dL when drawn around 8 a.m. That range matters because cortisol follows a strict daily rhythm. It peaks in the early morning hours, reaching its highest point about 30 to 45 minutes after you wake up, then gradually drops throughout the day. By 4 p.m., levels are significantly lower than the morning reading.
This natural rise-and-fall pattern is why doctors usually draw blood at specific times. A single random measurement doesn’t tell the full story. A morning value below 3 mcg/dL, combined with symptoms like chronic fatigue and weight loss, can point toward adrenal insufficiency, a condition where the glands aren’t producing enough cortisol. On the other end, levels that stay persistently elevated may signal overproduction.
Cortisol in Saliva
A small fraction of cortisol in your blood crosses into your saliva, and measuring it there has a practical advantage: you can collect samples at home without a needle. Your doctor may ask you to take several saliva samples throughout the day to map your personal cortisol curve, showing when it rises and falls. This is especially useful for catching problems that only show up at certain times.
Late-night salivary cortisol is one of the key screening tools for Cushing’s syndrome, a condition caused by prolonged cortisol excess. In a healthy person, cortisol drops to very low levels by bedtime. A sample collected between 11 p.m. and midnight should be below 100 ng/dL. In confirmed Cushing’s patients, late-night salivary cortisol can range from 100 to 6,000 ng/dL, sometimes dramatically higher than normal. The fact that sex plays a role in timing is worth noting too: the morning cortisol peak tends to hit around 30 minutes after waking in men and closer to 45 minutes in women.
Cortisol in Urine
Cortisol also filters through your kidneys into your urine. A 24-hour urine collection, where you save every drop of urine over a full day, gives doctors a picture of your total cortisol output rather than a snapshot at one moment. This smooths out the natural fluctuations and is particularly helpful when blood or saliva tests give borderline results. In some cases, a single morning urine sample is enough.
Cortisol in Hair
One of the newer and more revealing places to measure cortisol is in hair. As your hair grows, cortisol from your bloodstream gets incorporated into the shaft. Since hair grows about 1 centimeter per month, a 3 cm sample clipped close to the scalp represents roughly three months of cortisol exposure. This makes hair cortisol uniquely suited for assessing chronic stress, because blood and saliva only capture what’s happening in the moment or over a single day.
The measurement process is more involved than a simple blood draw. Hair samples are washed, ground or minced, and then the cortisol is chemically extracted and quantified in a lab. It’s a research tool that’s gaining clinical traction, particularly in studies on long-term stress, burnout, and conditions linked to prolonged cortisol elevation.
What Cortisol Does in the Body
Cortisol’s primary job is keeping energy available. When your body is under stress, whether from illness, injury, or psychological pressure, cortisol triggers your liver to produce glucose from non-sugar sources like amino acids. This process keeps blood sugar elevated so your muscles and brain have fuel. In animal studies, removing the cortisol response during stress cut the rise in blood glucose roughly in half compared to normal stress responses. Cortisol also prevents the liver from burning through its stored glycogen too quickly, preserving energy reserves for sustained demand.
Beyond energy management, cortisol acts as a powerful brake on inflammation. It dials down the production of certain inflammatory signaling molecules while boosting anti-inflammatory ones. This is why synthetic versions of cortisol are widely used to treat conditions involving excessive inflammation. The trade-off is that chronically elevated cortisol suppresses immune function more broadly, leaving you more vulnerable to infections over time.
Cortisol also influences how your body handles fat and protein. During periods of stress, it promotes the breakdown of proteins in muscle and other tissues, freeing up building blocks that the liver can convert into glucose. This is beneficial in short bursts but damaging when it persists, contributing to muscle wasting and changes in fat distribution, particularly the accumulation of fat around the midsection.
How Doctors Use Cortisol Tests
The choice of where to measure cortisol depends on what a doctor suspects. A morning blood draw is the standard first step for evaluating whether cortisol production is too low or too high. If the morning blood value falls above 13 to 18 mcg/dL (depending on the lab’s specific testing method), adrenal insufficiency is effectively ruled out. Below 3 mcg/dL with matching symptoms, and no further testing is needed to confirm the diagnosis.
For suspected Cushing’s syndrome, doctors often start with a suppression test. You take a small dose of a synthetic steroid at bedtime, which should signal your brain to shut down cortisol production by morning. If your morning cortisol still measures above 1.8 mcg/dL, the system isn’t responding to that “off” signal the way it should. This test catches about 95% of Cushing’s cases, though it produces some false positives, correctly ruling out the condition about 80% of the time.
Late-night salivary cortisol and 24-hour urine collections serve as complementary tools, each capturing a different dimension of cortisol behavior. Used together, these tests build a comprehensive picture of whether your body is producing the right amount of cortisol, at the right times, with the right responses to feedback signals.