Home > Understanding Cortisol

What is cortisol?

Mountains with sunrise.

The stress hormone

The chemical structure of cortisol.

Cortisol, sometimes called the stress hormone, is involved in many processes in the body, including the following:

  • Stress response

  • Immune response

  • Metabolism

Cortisol helps the body respond to stress or other external factors.

Without the ability to respond and adapt to these external factors, it would be impossible to maintain balance of physical, internal, and chemical conditions inside the body.


Image depicting five stress factors that cortisol helps regulate, including sleep, exercise, meal timing, body temperature, and stress

Get answers to frequently asked questions about cortisol, how it works in the body, and what causes excess cortisol.

View FAQs

Cortisol and the sleep-wake cycle

The sleep-wake cycle, also called the diurnal rhythm, influences the release of cortisol and other hormones. Cortisol is released in the body at different times throughout the day and night. Unless a person has an unusual sleep pattern (for example, shift work at night or regular sleep disturbances), cortisol should typically be at its lowest levels at night and its highest levels in the morning.

Graph showing normal diurnal rhythm with peak serum cortisol levels between 6 am and noon, with hypercortisolism maintaining higher levels with a peak between 4 pm and 8 pm

This regular rise and fall in cortisol levels supports the body’s natural tendency to feel tired at night and alert in the morning.

The HPA axis

The production of cortisol is controlled by the interaction between the hypothalamus, pituitary, and adrenal glands. This interaction is known as the HPA (hypothalamus–pituitary–adrenal) axis. Cortisol enters cells and binds to glucocorticoid receptors (GRs), which are located throughout the entire body. By binding to the GRs, cortisol makes changes so the body can respond to stress and other conditions in the environment.

Image of the hypothalamus, located in the brain

(a part of the brain)

Image of the pituitary, located in the brain near the hypothalamus

(located at the base of the brain)

Image of the adrenal glands, located above the kidneys

Adrenal glands​​​​​​
(located above the kidneys)

Image of glucocorticoid receptors in the cells throughout the body

Glucocorticoid receptor​​​​​​
(located in cells throughout the body)

How cortisol is produced in the body

Typically, the production of cortisol follows a specific process. Click on the steps below to learn more about how the body produces and regulates cortisol.

Expand All
STEP 1 Hypothalamus signals to pituitary
hypothalamus releases CRH Icon

When the hypothalamus senses the body needs more cortisol, it releases corticotrophin-releasing hormone (CRH) that signals to the pituitary gland.

STEP 2 Pituitary signals to adrenal glands
pituitary releases ACTH to signal adrenal glands

The pituitary gland responds to CRH by releasing a hormone called adrenocorticotropic hormone (ACTH) that signals to the adrenal glands.

STEP 3 Adrenal glands release cortisol
adrenal glands releasing cortisol

The adrenal glands release cortisol into the bloodstream.

STEP 4 Cortisol binds to cells
cortisol binds to glucocorticoid receptors

Cortisol travels throughout the body, entering cells and binding to glucocorticoid receptors (GRs).

STEP 5 Hypothalamus detects cortisol levels
hypothalamus reduces hormone signal

As cortisol levels rise in the body, the hypothalamus detects the increase and responds by reducing the level of CRH signaling the pituitary.

STEP 6 Pituitary decreases signaling to adrenal glands
pituitary releases hormone signal to adrenal glands

Reduced levels of the hormone CRH cause the pituitary gland to decrease the levels of ACTH signaling to the adrenal glands.

STEP 7 Adrenal glands decrease cortisol production
adrenal glands decrease cortisol production

In response to reduced levels of ACTH, the adrenal glands decrease the production of cortisol.

This tightly controlled feedback loop connects the brain to the rest of the body, which helps maintain homeostasis. Just like a thermostat adjusts the heating and cooling systems in a house to maintain an even temperature, the HPA axis adjusts the levels of cortisol in the body.

What causes excess cortisol?

Having too much cortisol in the body is known as hypercortisolism, also called Cushing syndrome. Typically, the feedback loop of the HPA axis regulates cortisol production and activity within the body. However, sometimes these hormone signals are disrupted, and excess cortisol may circulate in the body. If cortisol activity in the body does not go back to normal, this may lead to a number of serious health issues over time.

exogenous hypercortisolism icon

Exogenous hypercortisolism
(caused by factors outside the body)

Exogenous hypercortisolism

An excess of cortisol caused by factors outside the body is called exogenous hypercortisolism. Certain medications may affect cortisol levels by acting similarly to cortisol in the body. These medications, called corticosteroids (kawr-tuh-koh-ster-oids), are commonly used to treat conditions such as asthma, allergies, multiple sclerosis, and arthritis. When exposed to these medications long-term, the body may sometimes develop symptoms of hypercortisolism.

Endogenous hypercortisolism

An excess of cortisol caused by factors inside the body is called endogenous hypercortisolism. Unlike corticosteroids and other medications that act like hormones in the body, endogenous hormones are produced by the body itself. The cause of excess cortisol is typically a nodule located on either the pituitary or adrenal glands. These nodules may also occur elsewhere in the body (called an ectopic source).

Endogenous hypercortisolism icon

Endogenous hypercortisolism
(caused by factors inside the body)

What causes Cushing syndrome?

Depending on the source of excess cortisol, the diagnosis may have a more specific name. Cushing syndrome is an overarching term covering several distinct sources of excess cortisol. Cortisol-producing nodules—whether located in the pituitaryadrenal glands, or elsewhere in the body—may interfere with hormonal signaling in the HPA axis. This affects the body’s normal tightly controlled feedback loop, causing excess cortisol production and disrupting homeostasis.

Select from the options below to learn more about each potential cause of excess cortisol in the body.

pituitary nodule

Pituitary Cushing syndrome (also called Cushing disease)

Cause: A nodule in the pituitary gland causes increased production of the hormone ACTH, which stimulates the adrenal glands to make excess cortisol. This disrupts the feedback loop that controls cortisol levels within the body.

adrenal nodule

Adrenal Cushing syndrome (also called adrenal hypercortisolism)

Cause: A nodule on 1 or both of the adrenal glands causes too much of the hormone cortisol to be released into the bloodstream.

Outline of Body inside circle

Ectopic Cushing syndrome

Cause: Nodules that form outside the pituitary or adrenal glands are called ectopic. These nodules release the hormone ACTH, signaling the adrenal glands to produce too much of the hormone cortisol.

No matter the cause, Cushing syndrome may have serious health consequences. Learn more about its effects on the body.

See the Symptoms