Cortisol is produced by the adrenal glands, two small glands that sit on top of your kidneys. More specifically, it comes from the outer layer of each adrenal gland, called the adrenal cortex. But the adrenals don’t act alone. They take orders from your brain through a hormonal chain of command that starts in the hypothalamus, runs through the pituitary gland, and ends at the adrenals themselves.
Where Cortisol Is Made
Each adrenal gland has an outer cortex and an inner core. The cortex is divided into three zones, and cortisol production happens primarily in the middle zone, called the zona fasciculata. This layer makes up roughly 75% of the adrenal cortex and is packed with large, lipid-rich cells that store cholesterol, the raw material for cortisol. A thinner inner zone, the zona reticularis, also contributes some cortisol, though its main job is producing androgens.
Cortisol is a steroid hormone, which means it’s built from cholesterol rather than from proteins. Inside the cells of the zona fasciculata, cholesterol undergoes a series of chemical conversions. First, an enzyme clips off part of the cholesterol molecule to create a precursor called pregnenolone. From there, additional enzymes modify the molecule step by step until the final conversion happens inside the cell’s mitochondria, where the last enzyme transforms it into cortisol. The finished hormone is then released directly into your bloodstream.
The Brain’s Signaling Chain
Your adrenal glands don’t decide on their own when to make cortisol. They respond to a signaling system called the HPA axis, which connects three structures: the hypothalamus, the pituitary gland, and the adrenal glands.
The process works like a relay. When your brain detects something that requires a cortisol response (stress, low blood sugar, infection, intense exercise, or even extreme temperatures), the hypothalamus releases a signaling hormone called CRH. That hormone travels a short distance to the pituitary gland, a pea-sized gland at the base of the brain, and tells it to release ACTH into the bloodstream. ACTH then travels to the adrenal glands and locks onto highly specific receptors on the surface of cortisol-producing cells. Once ACTH binds, it triggers the cell to start converting cholesterol into cortisol.
This system also has a built-in brake. When cortisol levels in the blood rise high enough, the hypothalamus and pituitary detect that increase and dial back their signaling hormones. This negative feedback loop keeps cortisol from climbing unchecked under normal circumstances.
Other Signals That Boost Production
ACTH is the primary driver, but it’s not the only molecule that can stimulate cortisol release. Vasopressin, a hormone better known for helping your kidneys retain water, also plays a role. Research shows that vasopressin-containing cells exist within the adrenal gland itself, and vasopressin can directly stimulate cortisol secretion from adrenal tissue in a dose-dependent way. It appears to act as a local booster, amplifying cortisol output during acute stress when the body needs a rapid response.
Beyond hormonal signals, several everyday factors trigger the HPA axis to ramp up cortisol production: physical or emotional stress, vigorous exercise, infections, very hot or cold environments, and obesity. Even something as routine as waking up in the morning activates the system.
Cortisol’s Daily Rhythm
Cortisol production follows a predictable 24-hour cycle. Levels drop to their lowest point around midnight, often becoming nearly undetectable. They begin climbing between 2:00 and 3:00 a.m. while you’re still asleep, then peak at roughly 8:30 a.m. This morning surge is what helps you wake up alert and energized. From that peak, levels gradually decline through the afternoon and evening.
A standard blood test reflects this rhythm. Morning cortisol drawn between 6:00 and 8:00 a.m. typically falls between 10 and 20 mcg/dL. By 4:00 p.m., the normal range drops to 3 to 10 mcg/dL. Results outside these windows can be misleading if the timing of the blood draw isn’t factored in.
When the Body Makes Too Much
Sometimes cortisol production escapes the normal feedback loop. The result is a condition called Cushing’s syndrome, and it can come from several sources.
- Pituitary tumors: The most common internal cause. These are almost always noncancerous growths on the pituitary gland that produce excess ACTH, which in turn drives the adrenals to overproduce cortisol.
- Adrenal tumors: A tumor on the adrenal gland itself can independently churn out cortisol without waiting for signals from the brain. Most adrenal tumors are benign, though some are cancerous.
- Ectopic ACTH-producing tumors: Rarely, tumors in other organs (most often the lungs, but sometimes the pancreas, thyroid, or thymus) produce ACTH on their own. These tumors can be cancerous and tend to cause cortisol levels to spike rapidly.
The most common cause of Cushing’s syndrome overall, however, is external: long-term use of prescription corticosteroid medications, which mimic cortisol’s effects in the body.
When the Body Makes Too Little
The opposite problem, insufficient cortisol, occurs when the adrenal glands are damaged or when the pituitary gland fails to produce enough ACTH. The most well-known form is Addison’s disease, where the adrenal cortex itself is destroyed, usually by the body’s own immune system. Symptoms include persistent fatigue, muscle weakness, weight loss, and low blood pressure. Because cortisol helps regulate blood sugar, inflammation, and the stress response, even a moderate deficiency can affect how you feel throughout the day.