What does cortisol do to your body?

Cortisol affects almost every organ and tissue in your body. That sounds vague, so this page breaks it into the main jobs: the stress response, energy and blood sugar, inflammation and immunity, blood pressure, and the daily wake and sleep rhythm.

It describes what cortisol does when levels are normal, and what goes wrong at the extremes. It doesn’t cover treatment.

Cortisol

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The stress response

When something threatens you, two systems start. Adrenaline and noradrenaline act first, within seconds, to raise heart rate and blood pressure. Cortisol follows. A 2017 review says cortisol has to be built from cholesterol, so it lags the first response by several minutes (Endocrine Reviews, 2017).

The same review says cortisol then frees extra energy, improves circulation and distribution of oxygen to the muscles and brain, and stimulates alertness. Its job is to sustain the response and, as a 2018 review notes, its effects are longer lasting than those of the nerve-driven first phase (Front Behav Neurosci, 2018). See cortisol vs adrenaline for the comparison.

Energy and blood sugar

Glucocorticoids were named for their effect on glucose. The 2017 review says that during a stress response, cortisol raises glucose production in the liver, releases free fatty acids from fat stores and breaks down protein, so that fuel is available. It describes the same process on a daily schedule: the rise toward the end of the night frees energy from internal stores for the activity ahead.

The review adds that when cortisol stays high for a long time, the same actions work against you. It says chronically elevated cortisol promotes muscle breakdown and raises blood glucose. Read more in cortisol and blood sugar.

Inflammation and the immune system

MedlinePlus lists reducing inflammation (swelling) as one of cortisol’s jobs. A 2024 review says glucocorticoids have a broad range of immune-modulating and immune-suppressing effects, including inhibiting the activation of lymphocytes, a type of white blood cell, and reducing the signals that drive inflammation. It adds that many studies of these effects used much higher doses than the body makes on its own.

There is also a daily timing effect. The 2017 review says the early-morning rise in cortisol helps move certain white blood cells out of the blood and back to the bone marrow, with a delay of about 3 hours.

NIDDK notes that glucocorticoid medicines are used for conditions such as asthma, rheumatoid arthritis and lupus, and after organ transplant to suppress the immune system. Those medicines belong with a prescriber. Long-term excess of the body’s own cortisol also affects immunity: the 2024 review describes changes in white blood cells in Cushing’s syndrome that raise the risk of infections. See inflammation and cortisol.

Blood pressure and circulation

MedlinePlus and NIDDK both list blood pressure control among cortisol’s roles. The 2024 review explains part of the mechanism. Cortisol helps blood vessels respond to catecholamines such as adrenaline, and it supports the enzyme that makes adrenaline in the adrenal glands. The review says blood pressure changes are seen both when cortisol is too low and when it is too high. See cortisol and blood pressure.

The wake and sleep rhythm

Cortisol is part of how your body keeps time. It starts to rise in the second half of the night, peaks around waking and falls to its lowest at about midnight (Endocrine Reviews, 2024). The 2024 review says the relationship with sleep runs both ways: the daily rhythm of cortisol affects sleep timing and sleep stages, and sleep onset and sleep disruption affect the release of cortisol. For the full pattern, see when cortisol is highest and cortisol and sleep.

The brain, memory and mood

Cortisol also acts in the brain. The 2017 review discusses effects on memory and learning that depend on the time of day and the level. It says that when stress becomes chronic and cortisol stays high, particularly at the time of the usual low point, some of the beneficial actions invert, and that evidence from animals and humans links chronic exposure to modestly raised cortisol with memory deficits, among other effects. Much of the detailed work was done in animals. This page doesn’t claim that cortisol causes anxiety, depression or sleep problems. Where studies link them, the findings are associations. See cortisol and the brain.

What happens when levels are off

When cortisol is too high or too low for a long time, the effects show up as the symptoms of a medical condition.

• Too much over a long period (Cushing’s syndrome). MedlinePlus lists weight gain, thin arms and legs, a round face, easy bruising, wide purple streaks on the stomach, breasts, hips or under the arms, and muscle weakness. A 2024 review also links glucocorticoid excess with raised blood pressure, high blood sugar, abnormal blood fats, weaker immunity and thinning bones. See what high cortisol does.
• Too little (adrenal insufficiency). NIDDK lists long-lasting fatigue, muscle weakness, loss of appetite, weight loss and abdominal pain as the most common symptoms, plus low blood pressure that drops further on standing, low blood sugar and others. See low cortisol.

Each of these symptoms has many other causes. A single blood cortisol can’t diagnose or rule out either condition. If you take a steroid medicine, never stop it or change the dose on your own. Ask your prescriber.

Questions people ask

Is cortisol just a stress hormone?

No. It is sometimes called the stress hormone, and stress raises it. But it also follows a daily rhythm and supports energy, blood pressure and immune balance in the absence of stress. See is cortisol good or bad.

What does cortisol do in the morning?

It peaks. The 2017 review says the rise frees stored energy for the day, and researchers have argued that the rise after waking, called the cortisol awakening response, helps prepare the body for the day ahead (Front Neurosci, 2022). It also helps move certain white blood cells out of the blood. See the cortisol awakening response.

What does cortisol mean on a lab report?

It is the name of the test, and the number is the amount of cortisol in the sample. The meaning depends on the time of day, the lab and your medicines. See what is cortisol and normal cortisol levels.

Keep reading

• What is cortisol?

  The overview: where it comes from and why levels change.

• Is cortisol good or bad?

  Why it depends on how much, when and for how long.

• The HPA axis

  How the brain controls cortisol.

• Cortisol and the body

  Sleep, stress, blood sugar and more, one topic at a time.