What Does Cortisol Do in Dogs?

• Cortisol is an essential steroid hormone produced primarily by the adrenal glands.

• It forms part of the hypothalamic-pituitary-adrenal, or HPA, axis that regulates the body's response to stress.

• Cortisol increases the availability of energy, particularly glucose, when the body needs to respond to a challenge.

• It also influences inflammation, immune function, blood pressure, metabolism, and behavior.

• A temporary increase in cortisol during stress is normal and does not necessarily mean a dog is experiencing harmful stress.

• Repeated or prolonged stress can disrupt normal HPA-axis regulation, but chronic stress should not be confused with Cushing's disease.

• Persistently excessive cortisol occurs with conditions such as Cushing's syndrome, while inadequate cortisol production can occur with Addison's disease.

• Cortisol measurements need careful interpretation because timing, illness, excitement, sampling technique, and individual variation can all affect results.

Cortisol is a type of steroid hormone called a glucocorticoid. In dogs, it is produced mainly by the adrenal glands, two small glands located close to the kidneys.

Its release is controlled by a communication network called the hypothalamic-pituitary-adrenal axis, usually shortened to the HPA axis.

The sequence works roughly like this:

The hypothalamus in the brain detects that the body needs to respond to a challenge and releases corticotropin-releasing hormone, or CRH. This tells the pituitary gland to release adrenocorticotropic hormone, known as ACTH. ACTH travels through the bloodstream to the adrenal glands, stimulating them to release cortisol.

Cortisol then circulates throughout the body and affects numerous tissues.

Importantly, cortisol also helps switch its own production off. When sufficient cortisol is circulating, it provides negative feedback to the brain and pituitary gland, reducing further ACTH release. This feedback loop helps prevent the stress response from remaining permanently switched on.

It is an elegant biological thermostat when everything is working properly.

Calling cortisol simply a "stress hormone" undersells it considerably.

Cortisol participates in normal everyday physiology even when your dog is not obviously stressed. It helps maintain energy balance, influences cardiovascular function, modifies immune activity, and allows the body to adapt when circumstances change.

The easiest way to understand cortisol is to look at what happens when a challenge occurs.

Imagine your dog suddenly hears a loud crash behind them.

The nervous system responds almost immediately. Adrenaline and related chemicals help increase alertness, heart rate, and blood flow. The HPA axis follows, increasing cortisol.

Cortisol then helps keep the body supplied with the resources needed to respond.

If the noise turns out to be nothing more threatening than a saucepan falling onto the kitchen floor, the emergency passes and these systems should gradually return toward baseline.

That temporary physiological response is not inherently damaging. It is one of the mechanisms that has helped mammals survive unpredictable environments.

One of cortisol's major jobs during stress is ensuring that sufficient energy is circulating in the bloodstream.

Responding to a potential threat requires fuel. Muscles may need to move quickly, the brain needs glucose, and maintaining cardiovascular function requires energy.

Cortisol helps increase the availability of glucose by encouraging metabolic processes that make more fuel accessible. Experimental work in dogs has demonstrated that cortisol contributes significantly to the increase in circulating glucose and glucose production seen during a stress-hormone response.

In the short term, that is useful.

Imagine receiving an unexpected fire alarm. Your body's priority is not storing today's lunch efficiently for next week. It is making enough readily available energy available for you to react now.

Dogs operate under the same basic biological principle.

When cortisol remains excessively elevated for prolonged periods, however, those metabolic effects become less helpful. Chronic glucocorticoid excess can contribute to increased blood glucose, changes in fat distribution, muscle loss, and other metabolic abnormalities.

This is particularly obvious in dogs with Cushing's syndrome, where cortisol regulation is genuinely abnormal.

Cortisol also communicates extensively with the immune system.

Again, the relationship is more complicated than "cortisol suppresses immunity."

Short-term stress responses can redistribute immune cells and temporarily alter immune activity. Cortisol also helps prevent inflammatory reactions from becoming excessive.

That is one reason synthetic glucocorticoid medications such as prednisone or prednisolone are so effective at treating inflammatory and immune-mediated diseases. These medications essentially harness some of cortisol's biological effects at pharmacological doses.

But repeated or prolonged activation of stress systems can change immune regulation differently.

Research in dogs suggests that stressful experiences, including transportation, veterinary procedures, hospitalization, and prolonged shelter environments, can alter measurable immune responses. A recent canine study examining shelter stress also identified differences in lymphocyte populations and immune responsiveness associated with stress duration.

That does not mean every anxious dog automatically develops a "weak immune system." Biology is rarely that tidy.

It does mean that the nervous, endocrine, and immune systems communicate constantly, and prolonged stress can affect that conversation.

Cortisol does not simply circulate below the neck. It also affects the brain.

During an acute challenge, increased cortisol forms part of the body's wider state of alertness. This can influence attention, vigilance, learning, memory, and how strongly an animal responds to its surroundings.

A dog experiencing acute stress may therefore become more watchful, restless, reactive, or focused on potential threats.

Researchers frequently measure cortisol alongside behavioral signs when studying canine stress. For example, experimental studies have shown changes in salivary cortisol alongside behavioral and physiological responses such as altered heart or respiratory rates during stressful situations.

However, cortisol and behavior do not always match neatly.

A dog can look frightened without producing an enormous measurable cortisol response. Another dog may show substantial physiological activation while appearing relatively quiet.

That is one reason I would never assess a dog's emotional wellbeing from a cortisol measurement alone.

Not necessarily, and this is where the story gets more interesting.

Acute stress often causes cortisol concentrations to rise. This makes cortisol useful in stress research, particularly when researchers can compare measurements taken before and after a predictable event.

But chronic stress does not simply mean "high cortisol forever."

With prolonged or repeated activation, the HPA axis can adapt or become dysregulated. Different dogs may show different patterns depending on the stressor, duration, previous experiences, health, genetics, environment, and individual coping style.

A 2026 review of chronic stress in pet dogs emphasizes that prolonged stress involves dysregulation across multiple physiological and behavioral systems rather than one universally elevated hormone measurement.

This is important because cortisol is sometimes discussed online as though you could draw one blood sample, discover that it is high, and conclude that the dog has chronic emotional stress.

You cannot.

Researchers and veterinarians can measure cortisol using several biological samples, including blood, saliva, urine, feces, and hair.

They are not interchangeable.

Blood and saliva can provide information about cortisol around the time the sample is collected. Urinary cortisol reflects secretion across a somewhat broader period, while hair cortisol is being investigated as a potential measure of longer-term cortisol exposure.

Researchers have therefore become interested in hair cortisol when studying chronic stress.

A 2022 study followed shelter dogs during kenneling and after adoption using hair cortisol concentrations. The researchers found that hair analysis could provide useful information about longer-term cortisol exposure, but interpreting those values was considerably more complicated than simply categorizing them as "high stress" or "low stress."

Age, disease, medication, environment, hair characteristics, and previous stress exposure may all influence results.

Even saliva is not as straightforward as it first appears. A 2025 study involving adult pet dogs and assistance-dog puppies found that salivary cortisol was an unreliable substitute for simultaneously measured serum cortisol in those populations.

Cortisol is therefore a valuable biological clue, not a standalone emotional lie detector.

Absolutely.

This is something veterinarians need to consider when interpreting stress-related measurements.

Travel, strange smells, unfamiliar people, restraint, other animals, previous unpleasant experiences, and simply waiting in a veterinary environment can activate a dog's stress response.

One study of healthy dogs found increased serum cortisol alongside increased heart rate in dogs exposed to an indoor veterinary waiting-room environment.

This is also why low-stress handling techniques can be valuable even when a dog is not obviously terrified.

I have seen plenty of patients walk quietly into a consultation room while displaying subtler signs such as lip licking, scanning, increased panting, tense muscles, or suddenly refusing treats they normally love.

A dog does not have to be barking, shaking, or attempting to escape for their stress systems to be active.

There is an important difference between stress-related cortisol fluctuations and a medical condition causing sustained cortisol excess.

Persistent pathological cortisol excess is associated with hyperadrenocorticism, commonly called Cushing's syndrome or Cushing's disease.

In most affected dogs, the underlying problem is excessive ACTH production from a pituitary tumor. Less commonly, an adrenal tumor produces cortisol independently.

According to the Merck Veterinary Manual, pituitary-dependent disease accounts for approximately 80% to 85% of reported canine cases, with adrenal-dependent disease accounting for roughly 10% to 15%.

Typical signs of excessive cortisol exposure can include:

• Increased thirst and urination

• Increased appetite

• Panting and reduced heat tolerance

• Muscle weakness or wasting

• A pendulous or "pot-bellied" abdomen

• Hair thinning, hair loss, recurrent skin problems, or thin skin

Dogs may also develop high blood pressure and characteristic changes on blood and urine tests.

A stressed dog is therefore not automatically "developing Cushing's."

Cushing's is an endocrine disease involving abnormal cortisol regulation, not simply the end stage of everyday anxiety.

Dogs can also become seriously ill if they cannot produce enough cortisol.

The best-known example is hypoadrenocorticism, or Addison's disease.

Dogs with Addison's disease may lack glucocorticoids such as cortisol, mineralocorticoids such as aldosterone, or both.

The symptoms can be frustratingly vague. Dogs may experience reduced appetite, vomiting, diarrhea, weakness, lethargy, weight loss, or recurring episodes of apparently unexplained illness.

Some dogs suddenly become critically unwell during an Addisonian crisis, particularly when physiological demand increases and the body cannot mount an adequate adrenal response.

The definitive diagnosis generally involves an ACTH stimulation test, which examines whether the adrenal glands can produce cortisol when stimulated.

Addison's illustrates perfectly why cortisol should not be portrayed as something we simply want less of.

Dogs need enough cortisol, at the right time, under appropriate biological control.

When a dog encounters a short-lived challenge and then recovers, the stress-response system has done its job.

Problems are more likely when stressful events are frequent, unpredictable, unavoidable, or prolonged.

Examples could include persistent separation distress, repeated conflict with another animal, chronic pain, long-term kennel confinement, ongoing noise exposure, inability to rest properly, or repeated exposure to situations the dog finds frightening.

Over time, repeated HPA-axis activation can alter how the system responds.

Importantly, chronic stress does not always produce continuously high cortisol. Some animals may show altered baseline concentrations, changed reactivity to new stressors, or different recovery patterns.

This helps explain why modern canine welfare research increasingly combines physiological measurements with observations of behavior, environment, health, sleep, activity, and opportunities to perform normal behaviors.

There is no single magic "stress number."

I would frame the goal differently.

You do not need to suppress normal cortisol production. You want to reduce unnecessary or excessive activation of the systems producing it.

That starts with identifying why the dog is stressed.

A dog frightened by thunderstorms needs a different plan from a dog experiencing chronic orthopedic pain. A dog with separation anxiety needs something different again from a newly adopted dog still adjusting to an unfamiliar home.

Useful strategies may include predictable daily routines, adequate sleep, appropriate physical exercise, sniffing and enrichment opportunities, gradual behavior modification, reducing exposure to overwhelming triggers, treating underlying pain or disease, and giving the dog genuine opportunities to retreat and rest.

For significant anxiety, medication may also form part of an appropriate veterinary behavior plan.

The goal is not to engineer a dog who never experiences stress. Brief stress responses are normal.

The goal is resilience: the dog encounters a challenge, copes with it, and then returns toward physiological and emotional baseline instead of remaining stuck in a prolonged state of arousal.

Changes that pet parents interpret as "stress" occasionally turn out to have a medical explanation.

Book a veterinary examination if your dog develops persistent panting, dramatic appetite changes, increased drinking or urination, unexplained weight change, muscle weakness, recurrent vomiting or diarrhea, hair loss, skin changes, profound lethargy, or episodes of collapse.

Those symptoms can overlap with endocrine disorders and numerous other diseases.

Similarly, if anxiety or fear is having a significant impact on your dog's everyday life, do not assume that you simply need to "lower their cortisol."

Pain, neurological disease, gastrointestinal problems, sensory changes, endocrine disease, medication effects, and other medical conditions can all influence behavior.

Finding the underlying cause gives you a much better chance of helping the dog effectively.

Cortisol is not the villain of your dog's stress response. It is one of the hormones that makes that response possible.

When your dog encounters something challenging, cortisol helps make energy available, supports cardiovascular function, modifies immune activity, and prepares the body to cope. Once the challenge has passed, feedback mechanisms should reduce cortisol production and allow the system to settle.

The concern is not a temporary cortisol increase. It is prolonged or inappropriate activation, impaired recovery, or medical disease that disrupts normal cortisol regulation.

For pet parents, that means the most useful question usually is not, "How can I lower my dog's cortisol?"

It is, "Why is my dog's stress system being activated, and what can I change to help them feel safe and recover?"

That question takes us beyond one hormone and toward something much more important: the dog's overall physical health, emotional wellbeing, environment, and quality of life.