What is Cortisol? A Guide to the Body’s Stress Hormone

Cortisol is a steroid hormone, produced by your adrenal glands, that serves as your body’s primary stress hormone. 

While famously known for its role in the “fight-or-flight” response, its influence extends to nearly every organ and system, regulating metabolism, inflammation, blood pressure and even your sleep-wake cycle.

Chronic stress is a major public health issue, and its biological impact is often mediated by cortisol.

In fact, prolonged exposure to high cortisol levels is linked to a higher risk of numerous health problems, including heart disease, anxiety and depression.

Understanding cortisol is more than just understanding stress, it’s about understanding a key regulator of your body’s internal balance, or homeostasis.

This comprehensive guide will delve into the science behind this essential hormone. We will explore its crucial functions, the intricate system that controls its levels, and the symptoms and causes of both high and low cortisol.

Most importantly, you will learn about evidence-based strategies to manage your cortisol levels for better health and well-being.

Read on to become an expert on your body’s built-in alarm system.

What is Cortisol, Exactly?

At its core, cortisol is a steroid hormone belonging to a class of hormones called glucocorticoids.

It is synthesized and released by the adrenal glands, which are small, triangle-shaped organs located on top of each kidney.

Think of cortisol as a powerful, multi-talented manager within your body. While it’s most famous for its role as the primary stress hormone, this is just one of its many critical responsibilities.

According to the National Center for Biotechnology Information (NCBI), cortisol affects nearly every organ system. Its receptors are found in almost all cells in your body, which allows it to have widespread effects.

From influencing your mood and motivation to managing how your body uses energy, cortisol is essential for daily function and survival.

Your body has a sophisticated system to ensure its levels are just right—not too high and not too low—to maintain a stable internal environment, a state known as homeostasis.

Why is Cortisol Called the “Stress Hormone”?

Cortisol earned its nickname “the stress hormone” because of its central role in the body’s response to stress.

This response, often called the “fight-or-flight” response, is an ancient survival mechanism designed to prepare your body to either confront or flee from a perceived threat.

The Acute Stress Response

When you encounter a stressful situation—whether it’s a physical danger like a near-miss in traffic or a psychological one like a major work deadline—a specific part of your brain called the amygdala sends an alarm signal to your hypothalamus. This triggers a rapid cascade:

1. Initial Adrenaline Rush: The hypothalamus activates the sympathetic nervous system, prompting the adrenal glands to release adrenaline (also known as epinephrine). This is the hormone that causes your heart to pound, your breathing to quicken, and your senses to sharpen. It’s an immediate, high-octane energy boost.
2. Cortisol as Backup: If the brain continues to perceive the situation as a threat, the Hypothalamic-Pituitary-Adrenal (HPA) axis is activated. The adrenal glands then release cortisol. Cortisol’s job is to sustain the state of high alert. It floods the body with glucose (sugar) from your liver, providing a ready source of energy for your muscles.
3. Resource Management: As highlighted by WebMD, cortisol also curbs functions that would be non-essential or detrimental in a fight-or-flight situation. This includes suppressing the digestive system, the reproductive system and even growth processes. It ensures all available resources are directed toward survival.

Once the threat has passed, cortisol levels should fall and your body’s systems should return to normal.

This acute response is incredibly beneficial and necessary for navigating daily challenges.

The Problem with Chronic Stress

The issue arises when the stress is not a short-lived event but a constant presence. Modern life is filled with chronic stressors: financial worries, job pressure, relationship conflicts, or ongoing health issues.

When you’re under constant stress, the alarm button stays on.

This leads to prolonged exposure to elevated cortisol and other stress hormones. As the Mayo Clinic warns, this can disrupt almost all your body’s processes, putting you at increased risk for a wide range of health problems.

The system designed to save you in the short term can become harmful when it’s chronically activated.

What Are the Essential Functions of Cortisol Beyond Stress?

While its role in stress is paramount, cortisol is a workhorse hormone with several other vital functions that are crucial for your day-to-day health. It’s not a “bad” hormone, it’s essential for life.

Regulating Metabolism and Blood Sugar

Cortisol plays a key role in managing how your body uses carbohydrates, fats and proteins for energy. It ensures your brain has a constant supply of glucose, its primary fuel. As described by Cleveland Clinic, cortisol does this by:

• Increasing Gluconeogenesis: It stimulates your liver to produce glucose from non-carbohydrate sources, like amino acids.
• Modulating Insulin: It can decrease insulin’s effectiveness, preventing glucose from being stored in cells and keeping it available in the bloodstream for immediate use. This is helpful in a crisis but can contribute to high blood sugar over time.
• Acting on Tissues: It influences how muscle and fat tissues use glucose, prioritizing energy availability for critical functions.

Suppressing Inflammation

Cortisol is a potent anti-inflammatory agent. In short bursts, it can limit inflammation and help boost immunity.

This is why synthetic versions of cortisol, known as corticosteroids (like prednisone), are used to treat inflammatory conditions like asthma, allergies and autoimmune diseases.

However, the relationship is complex. A 2021 study published in Physiological Reviews notes that while acute cortisol release is anti-inflammatory, chronic elevation can lead to glucocorticoid resistance.

This means your immune cells become “deaf” to cortisol’s signals, which can paradoxically lead to increased inflammation and a weakened immune system.

Regulating Blood Pressure

Cortisol helps maintain normal blood pressure. It does this by increasing the sensitivity of your blood vessels to the effects of other hormones that constrict them (like adrenaline).

Chronically high cortisol levels can contribute to high blood pressure (hypertension), while abnormally low levels can cause low blood pressure (hypotension).

Controlling the Sleep-Wake Cycle

Cortisol follows a natural daily pattern known as a circadian rhythm. Its levels are typically lowest around midnight, begin to rise in the early morning hours (around 2-3 a.m.), and peak shortly after you wake up.

This morning surge, known as the Cortisol Awakening Response (CAR), helps you feel alert and ready to start your day.

Throughout the day, levels gradually decline, allowing you to wind down and fall asleep in the evening. Disruptions to this rhythm can lead to sleep problems and daytime fatigue.

How Does the Body Regulate Cortisol Levels? The HPA Axis

Your body doesn’t produce cortisol randomly. Its release is tightly controlled by a remarkable feedback system called the Hypothalamic-Pituitary-Adrenal (HPA) axis.

This axis is the command center for your stress response and cortisol regulation.

“The HPA axis is a complex set of direct influences and feedback interactions among three endocrine glands: the hypothalamus, the pituitary gland and the adrenal glands. It is a major neuroendocrine system that controls reactions to stress and regulates many body processes.” – Wikipedia

The process works like a thermostat:

1. The Hypothalamus Senses a Need: When your brain perceives a stressor or when cortisol levels in your blood are low, the hypothalamus releases Corticotropin-Releasing Hormone (CRH).
2. The Pituitary Gland Responds: CRH travels a short distance to the pituitary gland (often called the “master gland”) and signals it to release Adrenocorticotropic Hormone (ACTH) into the bloodstream.
3. The Adrenal Glands Get the Message: ACTH travels through your blood to the adrenal glands and stimulates them to produce and release cortisol.
4. The Negative Feedback Loop: As cortisol levels rise in the blood, it signals both the pituitary gland and the hypothalamus to decrease their production of ACTH and CRH, respectively. This negative feedback loop ensures that cortisol levels don’t spiral out of control and return to baseline once the stressor is gone.

For your cortisol levels to be healthy, all three parts of this axis—the hypothalamus, the pituitary gland and the adrenal glands—must be functioning correctly. Problems at any point in this chain can lead to either too much or too little cortisol.

What Are Normal Cortisol Levels?

Defining a “normal” cortisol level is complex because it fluctuates dramatically throughout the day and varies from person to person. What’s normal for a sample taken at 8 a.m. would be considered abnormally high if taken at 10 p.m.

Therefore, healthcare providers always interpret cortisol test results in the context of the time of day the sample was taken.

The following table provides typical reference ranges for different types of cortisol tests. It’s crucial to remember that these are just examples and the specific ranges used by the testing laboratory should always be consulted.

Test Type	Time / Condition	Typical Normal Range
Blood (Serum) Test	Morning (approx. 8 a.m.)	5 to 25 mcg/dL (138 to 690 nmol/L)
	Afternoon (approx. 4 p.m.)	3 to 16 mcg/dL (83 to 441 nmol/L)
Urine Test	24-hour collection	Less than 50-100 mcg/24 hours (varies by lab)
Saliva Test	Morning (upon waking)	Varies, but typically highest at this time
	Late Night (approx. 11 p.m.)	Very low, often less than 0.2 mcg/dL

Source: Ranges compiled from Mount Sinai, WebMD, and other clinical sources. These values are for informational purposes only.

What Causes High Cortisol Levels (Hypercortisolism)?

Having temporarily high cortisol is a normal response to stress. However, when your body is exposed to high levels for a prolonged period, it’s a condition known as hypercortisolism.

When this is caused by an underlying medical issue, it’s often called Cushing syndrome. The causes can be broadly divided into external (exogenous) and internal (endogenous) factors.

1. Chronic Stress

This is the most common reason for moderately elevated cortisol.

As discussed, a relentless barrage of psychological, emotional, or physical stressors keeps the HPA axis in a state of constant activation, leading to a steady overproduction of cortisol.

2. Medication Side Effects

The most frequent cause of Cushing syndrome is the long-term use of high-dose oral corticosteroid medications, such as prednisone, prednisolone, or dexamethasone.

These drugs are prescribed for a variety of conditions, including asthma, rheumatoid arthritis and lupus.

Since they mimic the effects of cortisol, they can lead to the same symptoms as if your body were overproducing it.

3. Pituitary Gland Tumors

A benign (noncancerous) tumor on the pituitary gland can produce an excess amount of ACTH. This overstimulates the adrenal glands, causing them to pump out too much cortisol.

This specific form of Cushing syndrome is known as Cushing’s disease and is the most common endogenous cause.

4. Adrenal Gland Tumors

A tumor, either benign or cancerous, on one of the adrenal glands can directly produce excess cortisol, independent of signals from the pituitary gland. In this case, ACTH levels would typically be low due to the negative feedback loop.

5. Ectopic ACTH-Producing Tumors

In rare cases, a tumor in another part of the body (such as the lungs, pancreas, or thyroid) can start producing ACTH. This is called an “ectopic” source, meaning it’s happening in an abnormal place.

This excess ACTH then stimulates the adrenal glands to overproduce cortisol.

What Are the Symptoms of High Cortisol?

The signs and symptoms of chronically high cortisol can be wide-ranging and affect many parts of the body. They can develop gradually and may be mistaken for other conditions.

According to sources like Healthline and the Mayo Clinic, the most common symptoms include:

Physical Symptoms:

• Weight gain, especially in the face (creating a “moon face”), around the midsection and between the shoulders (a “buffalo hump”).
• Skin changes, such as thinning skin that bruises easily, slowed healing of cuts, and the appearance of wide, purplish stretch marks (striae) on the abdomen, thighs and breasts.
• Muscle weakness, particularly in the upper arms and thighs.
• High blood pressure (hypertension).
• High blood sugar (hyperglycemia), which can lead to prediabetes or Type 2 diabetes.
• Bone loss (osteoporosis), leading to an increased risk of fractures.
• In women, excessive hair growth (hirsutism) on the face and body, and irregular or absent menstrual periods.
• In men, decreased libido, erectile dysfunction and reduced fertility.

Psychological and Cognitive Symptoms:

• Severe fatigue and a feeling of being “wired but tired”.
• Irritability, anxiety or depression.
• Difficulty concentrating and memory problems (“brain fog“).
• Trouble sleeping (insomnia).

What Are the Long-Term Health Risks of High Cortisol?

Untreated hypercortisolism is not just a matter of uncomfortable symptoms, it poses serious long-term health risks. The constant strain on your body’s systems can lead to significant complications.

• Cardiovascular Disease: The combination of high blood pressure, high blood sugar, and increased inflammation significantly raises the risk of heart attacks, strokes, and other cardiovascular events.
• Type 2 Diabetes: By interfering with insulin’s function, high cortisol can directly lead to insulin resistance and the development of Type 2 diabetes. Research suggests that hypercortisolism may be present in 3-8% of patients with Type 2 diabetes.
• Osteoporosis: Cortisol decreases bone formation and increases bone resorption, leading to weak, brittle bones that are prone to fractures.
• Weakened Immune System: While acutely anti-inflammatory, chronic high cortisol suppresses the immune system, making you more susceptible to infections.
• Mental Health Disorders: The link between chronic stress, cortisol and mental health is well-established. Prolonged exposure can contribute to the development or worsening of major depressive disorder and anxiety disorders.
• Cognitive Decline: Studies, such as one published in Neurology, have linked higher cortisol levels with impaired memory and lower brain volumes, even in younger to middle-aged adults.

What Causes Low Cortisol Levels (Hypocortisolism)?

Just as too much cortisol is harmful, too little can also be dangerous.

Abnormally low cortisol levels, a condition called hypocortisolism or adrenal insufficiency, means your body can’t respond properly to stress and may struggle to perform its basic functions.

Primary Adrenal Insufficiency (Addison’s Disease)

This occurs when your adrenal glands themselves are damaged and cannot produce enough cortisol.

The most common cause in developed countries is an autoimmune reaction, where the body’s own immune system attacks the adrenal cortex.

This specific condition is known as Addison’s disease. Other less common causes include infections (like tuberculosis), cancer that has spread to the adrenal glands, or bleeding into the glands.

Secondary Adrenal Insufficiency

This form of adrenal insufficiency happens when the pituitary gland doesn’t produce enough ACTH. Without the ACTH signal, the adrenal glands don’t get the message to make cortisol.

Causes can include a pituitary tumor, pituitary surgery or radiation, or head trauma. A common cause is the abrupt stopping of long-term corticosteroid medication.

The body had gotten used to an external source of cortisol-like hormones, so the HPA axis “went to sleep” and needs time to wake up and start producing its own again.

What Are the Symptoms of Low Cortisol?

The symptoms of adrenal insufficiency often develop slowly over months and can be vague, making diagnosis challenging. They include:

• Chronic, worsening fatigue that is not relieved by sleep.
• Muscle weakness.
• Unintentional weight loss and loss of appetite.
• Low blood pressure (hypotension), which can cause dizziness or fainting upon standing.
• Nausea, diarrhea or vomiting.
• Abdominal pain.
• Craving for salty foods (especially in Addison’s disease, where aldosterone is also low).
• Hyperpigmentation, or darkening of the skin, especially in skin creases, on scars, and on the gums (a classic sign of Addison’s disease).

A sudden, severe worsening of these symptoms can lead to an adrenal crisis, a life-threatening medical emergency characterized by shock, seizures, and coma, which requires immediate medical attention.

How is a Cortisol Test Performed?

Because cortisol levels fluctuate, a single measurement is often not enough for a diagnosis. A healthcare provider will choose one or more tests based on your symptoms to get a clear picture of your cortisol production.

1. Blood Test

A serum cortisol test measures the total amount of cortisol in your blood.

Since levels follow a circadian rhythm, blood is typically drawn twice: once in the morning (around 8 a.m.) when levels should be high, and again in the afternoon (around 4 p.m.) when they should be lower.

A lack of this daily variation can be a sign of a problem.

2. 24-Hour Urinary Free Cortisol Test

This test measures the amount of cortisol excreted in your urine over a full 24-hour period. It provides a good assessment of the total cortisol production throughout the day, averaging out the hourly fluctuations.

You will be given a special container and instructed to collect all of your urine for 24 hours.

3. Late-Night Salivary Cortisol Test

This is a simple, non-invasive test you can do at home. You collect a sample of your saliva by chewing on a swab late at night (usually between 11 p.m. and midnight).

In healthy individuals, cortisol levels should be very low at this time. An elevated late-night salivary cortisol level is a strong indicator of Cushing syndrome.

4. Hair Cortisol Test

A more recent and innovative method, the hair cortisol test provides a look at long-term, cumulative cortisol exposure.

As explained by the UCSF Stress Measurement Network, as hair grows (about 1 cm per month), cortisol from the bloodstream is incorporated into the hair shaft.

Analyzing a small sample of hair from the scalp can provide an average cortisol level over the past several months, making it an excellent biomarker for chronic stress.

How Can You Lower Cortisol Levels Naturally?

If your high cortisol is due to a medical condition like a tumor, medical treatment is necessary.

However, if it’s driven by chronic stress, lifestyle modifications can be highly effective.

These strategies work by helping to down-regulate the HPA axis and promote a state of relaxation.

1. Adopt a Nutrient-Dense Diet

What you eat directly impacts your hormones. Focus on a whole-foods diet rich in anti-inflammatory compounds.

• Limit Sugar and Processed Foods: High-sugar diets can spike cortisol.
• Eat Complex Carbohydrates: These provide a steady supply of energy without the sharp blood sugar swings.
• Focus on Omega-3s and Magnesium: Foods like fatty fish, nuts, seeds, and dark leafy greens are rich in these nutrients, which have been shown to help regulate cortisol.
• Stay Hydrated: Dehydration itself can be a physical stressor that raises cortisol.

2. Prioritize Quality Sleep

Sleep and cortisol have a reciprocal relationship. Poor sleep raises cortisol, and high cortisol can disrupt sleep.

Aim for 7-9 hours of quality sleep per night. Improve sleep hygiene by maintaining a consistent schedule, creating a dark and cool environment, and avoiding screens before bed.

3. Engage in Regular, Mindful Exercise

Regular physical activity is a powerful stress-reducer. However, over-exercising (intense, prolonged workouts without adequate rest) can actually increase cortisol.

The key is balance. Activities like walking, yoga, tai chi, and light jogging are excellent for managing stress without over-taxing the body.

4. Practice Stress-Management Techniques

Actively engaging in relaxation can help turn off the “fight-or-flight” response. A meta-analysis published in 2024 confirmed that stress management interventions are effective in changing cortisol levels.

• Mindfulness and Meditation: These practices train your brain to be less reactive to stressful thoughts.
• Deep Breathing Exercises: Slow, deep diaphragmatic breathing activates the parasympathetic nervous system, your body’s “rest and digest” system, which directly counteracts the stress response.
• Spending Time in Nature: Often called “forest bathing”, spending time in a natural environment has been shown to lower cortisol levels.

5. Nurture Social Connections

Positive social interaction and feeling a sense of belonging can buffer the effects of stress. Spending quality time with loved ones, laughing, and physical touch (like hugging) can all help lower cortisol.

When Should You See a Doctor About Your Cortisol Levels?

While daily stress is normal, you should contact a healthcare provider if you experience persistent symptoms that suggest a potential cortisol imbalance. It’s important not to self-diagnose, as these symptoms can overlap with many other conditions.

Frequently Asked Questions (FAQ)

1. Can high cortisol cause anxiety?

Yes. Cortisol is designed to put your body on high alert. Chronically elevated levels can keep your nervous system in a state of “fight-or-flight”, directly contributing to feelings of anxiety, irritability and being constantly on edge.

2. Does coffee raise cortisol levels?

Yes, caffeine intake can cause a temporary spike in cortisol levels, especially in people who don’t consume it regularly. The effect is generally short-lived, but for those already under chronic stress, it may be wise to moderate caffeine intake.

3. What is the difference between cortisol and adrenaline?

Adrenaline provides the immediate, rapid-fire response to stress (fast heart rate, energy surge). Cortisol is the follow-up hormone, it’s released more slowly and sustains the stress response, managing energy stores and keeping the body on high alert for a longer period.

4. How quickly can you lower cortisol?

You can lower cortisol acutely within minutes through techniques like deep breathing or meditation. However, lowering chronically elevated cortisol levels through lifestyle changes like diet, exercise and better sleep is a gradual process that can take weeks to months.

5. Is cortisol a “bad” hormone?

No, cortisol is absolutely essential for life. It regulates metabolism, inflammation, blood pressure, and the sleep-wake cycle. The problem is not the hormone itself, but the imbalance caused by having consistently too much or too little of it.

6. What is the Cortisol Awakening Response (CAR)?

The CAR is the sharp increase in cortisol levels that occurs in the first 30-45 minutes after waking up. This natural morning surge helps to promote alertness, mobilize energy, and prepare your body for the demands of the day.

7. Can you have high cortisol and not be stressed?

Yes. While chronic stress is a common cause, high cortisol can also be caused by underlying medical conditions like pituitary or adrenal tumors (Cushing syndrome) or as a side effect of certain medications, even if you don’t feel psychologically stressed.

8. Does cortisol make you gain belly fat?

Yes, chronically high cortisol is strongly linked to an increase in visceral fat, which is the fat stored deep within the abdominal cavity around your organs. This is one of the hallmark signs of hypercortisolism.

Conclusion

Cortisol is far more than just a simple “stress hormone”. It is a dynamic and essential regulator of your body’s most critical functions.

From waking you up in the morning to managing your energy and controlling inflammation, a healthy cortisol rhythm is fundamental to your well-being.

While the acute stress response is a life-saving mechanism, the pressures of modern life can turn this system against us, leading to chronic elevation and a host of health problems.

The key takeaway is that you have a significant degree of influence over your cortisol levels.

By prioritizing sleep, adopting a balanced diet, engaging in regular movement and actively practicing stress-reduction techniques, you can help restore balance to your HPA axis.

If you suspect a more serious imbalance, don’t hesitate to seek professional medical advice.

What is your biggest challenge when it comes to managing stress? Share your thoughts or questions in the comments below—let’s learn from each other!