What Is Cortisol: Hero or Villain?

Cortisol is a steroid hormone produced by your adrenal glands in response to stress, and it touches almost every system in your body.

In this article, we’ll go through what cortisol is, what it does, what happens when levels run too high, and why this misunderstood molecule is both essential to life and potentially harmful.

This article is from the Lifestyle section of our Library.

You've probably heard cortisol described as "the stress hormone" — something to be crushed, detoxed, or suppressed at all costs. But that framing misses the truth. Cortisol is one of the most important things your body makes.

Without it, you couldn't get out of bed in the morning, respond to an emergency, or fight infections. The real question isn't whether cortisol is good or bad. It's whether your cortisol is doing the right thing, at the right time, in the right amount.

What Is Cortisol?

Cortisol is a hormone, a steroid, and a glucocorticoid — and all three labels are correct. It's a hormone because it's released into the bloodstream to keep tissues and organs healthy. It's a steroid because it's synthesised from cholesterol (just like testosterone) and shares the same chemical structure that all steroid molecules do.

It's a glucocorticoid: the most important one the human body makes. Its primary role involves regulating “glucose” (blood sugar). And the "corticoid" part of that name tells you where it's made: the cortex, or outer layer, of the adrenal glands, which sit on top of each kidney.

How Is Cortisol Made?

Your brain controls how much cortisol you make. When your brain detects a “stressor”, be it physical (like exercise or extreme temperatures), physiological (like an illness, infection, sleep or nutrition deprivation) or psychological (like work pressure, financial worries, bereavement, loneliness or conflicts), it sends a signal down to your adrenal glands that tells them to start making and releasing cortisol [1].

It’s not all negative, though. Cortisol can even rise (moderately) in excitement or anticipation of something good — it's a response to “arousal”, not just negative stressors.

There is always cortisol in your system, so you are always making it, but it doesn’t stay flat throughout the day either. Like your sleep hormones, cortisol also follows a semi-regular pattern throughout the day (a “circadian rhythm”).

Cortisol (ideally) should be at its lowest in the evening and before you go to bed. It then begins to rise in the early morning hours and peaks within the first hour of waking — known as the “cortisol awakening response” [2].

As much as it may feel like it, that early morning cortisol spike isn’t a sign of stress; it’s the body’s natural alarm clock.

It gets your metabolism, immune system and brain going ready for the day. Problems arise when this rhythm becomes disrupted — which is where cortisol’s bad reputation comes from.

What Does Cortisol Do to the Body?

Cortisol's main job is to mobilise “resources” when your body needs them most [3].

This includes: raising your blood sugar levels, which you need if you detect a threat you need to run from. It also helps control how much fat you are storing and burning, and your appetite.

Controlling your immune response from getting out of control; this is why “synthetic cortisols” (like hydrocortisone and prednisone) are prescribed to control inflammation.

Cortisol keeps your blood flowing when it’s needed by controlling your blood pressure and fluid balance in your body. It helps your brain store memories, process emotions correctly and keep you alert, which is why it can affect your mood and cognitive function when out of control.

So is Cortisol Good or Bad?

The honest answer is both. Acute cortisol “spikes”, the kind that last minutes to an hour, are genuinely protective and necessary.

However, consistently elevated cortisol is not good. The difference between cortisol as hero and cortisol as villain is almost entirely a matter of how long the “spike” is!

How to Tell If You Have High Cortisol

When cortisol runs high for a long time, whether it's from work, overtraining, poor sleep, or a medical condition, it goes on to affect your body in the same way.

“Cognitively”

You may notice brain fog, difficulty concentrating, and poor memory. Many people describe feeling "wired but tired" — mentally restless yet physically exhausted.

“Emotionally”

It is linked to anxiety, irritability, and low mood. It does this by reducing activity in the rational part of your brain (your “prefrontal cortex”) while increasing activity in the threat-detection system (your “amygdala”)[4].

“Physically”

Symptoms can include poor sleep quality, increased appetite (particularly for high-fat and high-sugar foods), muscle weakness, slow recovery from exercise or illness, getting ill more often, and skin damage.

Cortisol, Weight Gain & "Cortisol Belly"

Cortisol does promote fat storage, and even worse, it drives fat around your internal organs (“visceral fat”). This is sometimes called “cortisol belly” and is one of the worst types of fat, being linked to several serious health conditions [5].

Cortisol also causes you to gain fat by redirecting the energy you eat away from places where it can be burned to places where it is stored (like your belly, legs, arms and hips).

Thirdly, cortisol also stimulates your appetite, particularly cravings for calorie-dense “comfort foods”.

So: yes. Consistently elevated cortisol can give you a “cortisol belly” and make you gain weight. But not on its own. Diet, physical activity, sleep quality and genetics also play a role.

How Long Does (or should) it take Cortisol to Return to Normal?

How long is a spike, and when does a spike turn into a problem? There is no exact answer, but after being exposed to a stressor, cortisol typically returns to normal levels within 60-90 minutes.

The speed of the recovery will depend on how intense or long the stressor is, how you react to it, how well or fit you are, and your social support and environment [6].

There are things you can do to reduce your cortisol spikes and return them to normal levels more quickly. Persistent stressors that appear in your life all too frequently are hard to resolve because you can never fully switch off your cortisol response.

This is why sustained stress (like from work, relationships or financial insecurity) can keep cortisol elevated for weeks or months. The best thing you can do is to (if you can) avoid these in the first place.

Frequently Asked Questions About Cortisol

Does cortisol increase blood pressure?

Yes, it raises your blood pressure by making your blood vessels more receptive to the blood vessel-constricting hormone adrenaline.

Does cortisol reduce testosterone?

Yes, it shuts down testosterone production by using up some of the things that make it and suppressing the processes that stimulate testosterone production. This exacerbates things like fatigue, bad mood, libido and recovery from exercise [7].

Does cortisol affect sleep?

Yes, poor sleep raises cortisol, and elevated cortisol disrupts sleep — it’s a vicious cycle. It does this by suppressing melatonin (the “sleep hormone”). Read how to fix your sleep problems and break the cycle.

Does cortisol cause hair loss?

Yes, but indirectly. Too much stress and cortisol damage your hair follicles prematurely. The good news is that your hair typically regrows once your stress levels are back to normal [8].

Does cortisol cause acne?

Yes, but indirectly. It stimulates your skin glands to produce more oil and hormones that cause acne. Acne flares are a well known stress-response and one of the most common causes of it.

Does cortisol cause inflammation?

Cortisol is actually anti-inflammatory. When it is chronically elevated you body becomes resistant to it, and it starts exacerbating (disease-causing) low-grade inflammation [9].

Does cortisol cause anxiety?

High cortisol and anxiety are tightly linked. Cortisol makes changes to your brain, which predisposes you to anxious thinking. Anxiety, in turn, stimulates cortisol activity — yet another vicious cycle [4].

Sources

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2. Adam EK et al. "Diurnal cortisol slopes and mental and physical health outcomes: A systematic review and meta-analysis." Psychoneuroendocrinology. 2017;83:25–41. PMID: 28578301

3. Kaur J et al. Physiology, Cortisol. [Updated 2025 Dec 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538239/

4. McEwen BS. "Neurobiological and systemic effects of chronic stress." Chronic Stress. 2017;1:2470547017692328. PMID: 28856337

5. Björntorp P. "Do stress reactions cause abdominal obesity and comorbidities?" Obesity Reviews. 2001;2(2):73–86. PMID: 12119665

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