How Chronic Stress Affects a Dog's Body

• Short-term stress is normal and useful, but problems can develop when stress is frequent, prolonged, or the dog has little opportunity to recover.

• Chronic stress involves ongoing changes in systems including the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system.

• Stress hormones such as cortisol affect much more than mood. They influence metabolism, immune activity, digestion, cardiovascular function, and brain function.

• Chronically stressed dogs may develop changes in sleep, appetite, digestion, activity, learning, and social behavior.

• Stress can alter immune responses, although it is too simplistic to say that stress merely “switches off” the immune system.

• Long-term stress does not necessarily mean permanently elevated cortisol. Chronic stress can produce more complex changes in how the stress-response system functions.

• Persistent behavioral changes should never automatically be blamed on anxiety. Pain, gastrointestinal disease, endocrine disorders, neurological disease, and other medical problems can look remarkably similar.

Two major biological systems become particularly important when a dog perceives a threat.

The first is the sympathetic nervous system, which is responsible for many of the rapid changes we associate with the fight-or-flight response. Adrenaline and related chemicals increase heart rate, redirect blood flow, sharpen attention, and make fuel available for immediate action.

The second is the hypothalamic-pituitary-adrenal axis, usually shortened to the HPA axis.

Think of this as a hormonal relay system between the brain and adrenal glands.

The hypothalamus in the brain signals the pituitary gland, which releases adrenocorticotropic hormone (ACTH). ACTH then tells the adrenal glands to release cortisol.

Cortisol helps maintain blood glucose, influences metabolism, modifies immune activity, and prepares the body to deal with a challenge. These effects are extremely useful in the short term.

Research reviews of cortisol in dogs emphasize that cortisol is a normal and essential hormone rather than simply a “stress hormone.” Problems arise when regulation of this system becomes disrupted or repeatedly activated over long periods.

Read the 2024 review of cortisol physiology and stress in dogs on PubMed

Imagine a dog who is startled when something falls from a kitchen counter.

Their heart races, they jump, they investigate the noise, and five minutes later they are asleep on the sofa.

That is very different from a dog who spends hours every day worried about being left alone, reacting to noises outside, repeatedly clashing with another household dog, or living with untreated pain.

With chronic stress, the problem is not necessarily the intensity of one stressful event. It is the frequency, duration, unpredictability, and lack of recovery between events.

A major recent review of chronic stress in pet dogs describes prolonged dysregulation of stress-response systems as potentially affecting both health and behavior. It also highlights something owners sometimes overlook: stress can arise not just from obvious fear but from repeatedly unmet physical, social, safety, or cognitive needs.

That distinction matters. A dog does not need to look terrified all day to be struggling with chronic stress.

The brain is both the control center for the stress response and one of the organs affected by it.

During an immediate threat, attention narrows toward whatever seems important for survival. This is one reason a frightened dog may appear to “forget” cues they normally know perfectly well.

If that state happens repeatedly, behavior can become increasingly biased toward detecting and responding to potential threats.

A dog may:

• startle more easily

• become increasingly watchful

• struggle to concentrate

• react more strongly to comparatively minor events

• recover more slowly once frightened

This can create a frustrating cycle. The dog becomes more reactive, their environment subsequently contains more stressful encounters, and their stress system receives even fewer opportunities to settle.

Researchers have even identified measurable behavioral differences in dogs described as chronically stressed. A 2023 study found changes in behavioral laterality, or side preference, in chronically stressed dogs compared with emotionally and physically healthy dogs, adding to evidence that prolonged stress can influence brain function and behavior.

See the chronic stress and behavioral laterality study on PubMed

Sleep and stress have a particularly close relationship.

A relaxed dog should spend a substantial amount of the day resting and sleeping. Dogs vary considerably, but many adults comfortably sleep or rest for well over half of each 24-hour period.

A chronically vigilant dog may technically lie down without obtaining the same quality of restorative rest. They may repeatedly wake, monitor sounds, follow their owner from room to room, or sleep lightly enough that small environmental changes disturb them.

Poor sleep can then make emotional regulation harder.

Anyone who has tried to function after several nights of broken sleep knows that patience and concentration become thinner. Dogs cannot tell us that they feel mentally exhausted, but tired dogs can similarly become more irritable, impulsive, or easily overwhelmed.

This is why improving sleep is often an important part of treating anxiety and chronic stress, rather than merely a pleasant side effect.

The brain and digestive system communicate constantly through what is commonly called the gut-brain axis.

Stress can alter gastrointestinal movement, secretion, intestinal permeability, appetite, and microbial communities within the digestive tract. Meanwhile, signals arising from the gastrointestinal system can influence the brain.

In practical terms, this helps explain why some anxious dogs develop loose stool, urgent defecation, nausea, reduced appetite, or occasional vomiting during stressful periods.

That does not mean every digestive problem is caused by anxiety.

As a veterinarian, this is an important distinction I would never want an owner to miss. A dog with recurrent diarrhea may be stressed, but they could also have parasites, dietary intolerance, inflammatory gastrointestinal disease, pancreatic disease, infection, or any number of other medical conditions.

Stress should therefore be considered one part of the clinical picture rather than used as a convenient explanation for persistent digestive signs.

The immune system communicates extensively with both the nervous system and endocrine system.

Stress hormones act on immune cells through glucocorticoid and adrenergic receptors. Consequently, stress can alter inflammation, immune-cell activity, and responses to infectious or inflammatory challenges.

This relationship is considerably more complicated than the popular phrase “stress lowers immunity.”

Sometimes stress increases certain inflammatory pathways while suppressing others. The effect depends on factors including the duration and intensity of stress.

Studies in dogs provide evidence that stressful environments can measurably influence immune responses. For example, research involving shelter dogs has identified differences in lymphocyte populations and immune responsiveness associated with environmental stress and duration of sheltering.

Earlier research has also shown that transportation, veterinary procedures, and hospitalization can alter immune parameters in healthy dogs, illustrating just how closely stress physiology and immune function interact.

Read the canine stress and immune-function study on PubMed

For an individual pet dog, however, we cannot reliably say that stress will automatically lead to more infections or a particular inflammatory disease. The science supports immune modulation, not a simple one-way suppression of immunity.

Cortisol helps ensure that energy is available during demanding situations.

Among other effects, it influences how the body handles glucose, protein, and fat. In the short term, that makes perfect biological sense: an animal facing a threat needs readily accessible fuel.

Long-term disruption of this system is less helpful.

Some chronically stressed dogs lose interest in food. Others appear hungrier. Some experience changing body weight or digestive patterns.

However, metabolic changes should again be interpreted cautiously. Increased thirst, increased appetite, weight changes, panting, muscle loss, or changes in coat quality can also occur with endocrine diseases, including hyperadrenocorticism, commonly known as Cushing's disease.

Chronic psychological stress and Cushing's disease are therefore not interchangeable simply because cortisol is involved in both.

During stress, the body prioritizes immediate action.

Heart rate and blood pressure may increase, respiration becomes faster, and circulation changes to support muscles and organs needed for rapid activity.

Brief increases are normal.

Repeated sympathetic activation, however, means the cardiovascular system is being asked to respond again and again. In other species, chronic stress is strongly associated with adverse cardiovascular effects.

The long-term clinical consequences are less clearly established in pet dogs, so I would avoid claiming that anxiety directly causes specific canine heart diseases. What we can say is that chronic stress repeatedly changes cardiovascular physiology and adds to the body's overall physiological workload.

Dogs with existing heart or respiratory disease may therefore tolerate episodes of intense stress particularly poorly.

Skin problems and stress can become another chicken-and-egg situation.

Itching is stressful.

Stress can also increase behaviors such as licking, chewing, scratching, and self-grooming. Those behaviors can further irritate already inflamed skin.

Research in dogs with atopic dermatitis has explored hair cortisol as a potential marker linking disease severity, stress, and quality of life. The relationship remains complex, but the work reinforces the close interaction between chronic physical disease and emotional wellbeing.

See the canine atopic dermatitis and hair cortisol study on PubMed

This is one reason good veterinary treatment for chronic skin disease is not merely about making the skin look better. Breaking the itch-stress-scratch cycle can considerably improve a dog's quality of life.

An anxious dog's body is often doing more work than it appears to be doing.

Pacing, panting, trembling, repeatedly standing and lying down, monitoring windows, responding to noises, and remaining physically tense all require energy.

Dogs living in prolonged states of arousal may therefore appear exhausted once they finally relax.

Muscular tension can potentially add another layer of discomfort, particularly in older dogs or those with orthopedic disease.

This interaction often runs both ways. Pain makes dogs more vulnerable to stress, while stress can make coping with pain harder.

In clinical practice, this is why a dog who suddenly becomes irritable, restless, clingy, reluctant to settle, or reactive should not automatically be labeled as “anxious.” Pain is one of the first medical possibilities worth considering.

Owners are often more likely to notice behavioral changes than physical ones.

A chronically stressed dog may become clingier, more withdrawn, more reactive, or unusually quiet.

Some dogs start barking at things they previously ignored. Others hide, follow their owners constantly, struggle when left alone, guard resources, become reluctant to play, or lose interest in activities they previously enjoyed.

A dog's tolerance for everyday frustrations can also shrink.

I often describe this using the idea of a bucket. Every stressful event adds a little water: poor sleep, construction noise, discomfort from arthritis, an unfamiliar visitor, another dog barking outside, then the delivery driver appearing at the door.

No single event necessarily fills the bucket.

Once it is already close to the top, though, one comparatively small trigger can cause it to overflow.

That is why apparently “random” behavioral explosions often make considerably more sense when we look at everything that happened during the previous hours or days.

No, and this is an important misconception.

Cortisol is released in patterns rather than remaining at one fixed level. Concentrations vary with time of day, activity, health, environment, and the method used to measure them.

Furthermore, chronic stress does not necessarily produce permanently elevated cortisol.

Long-lasting or repeated activation of the HPA axis can eventually alter the regulation of that system. Researchers studying canine hair cortisol have even noted that prolonged stress may sometimes be associated with reduced rather than elevated cortisol activity.

In other words, chronic stress is better understood as dysregulation of the stress-response system, not simply “too much cortisol.”

Hair cortisol is particularly interesting because hair potentially reflects cortisol exposure over a longer period than a single blood or saliva sample.

A 2022 study following shelter dogs found that hair cortisol concentrations were significantly higher after six weeks in the shelter than before admission and after adoption, providing objective evidence that prolonged environmental circumstances can influence longer-term cortisol patterns.

Read the shelter-dog hair cortisol study on PubMed

There is rarely one universal cause.

Potential contributors include persistent pain, separation-related distress, noise sensitivity, conflict between household pets, unpredictable handling, frequent punishment, insufficient sleep, inability to escape unwanted interactions, lack of appropriate exercise or enrichment, repeated exposure to frightening situations, and major environmental changes.

Physical illness itself can also become a chronic stressor.

Individual differences matter enormously. One dog may happily sleep through a busy household while another struggles with the constant movement and noise.

Breed, genetics, early experiences, previous trauma, health, age, social relationships, and temperament can all influence how strongly a dog responds.

The relevant question is therefore not simply, “Would most dogs find this stressful?”

It is, “Is this dog coping with it?”

The first step is identifying and reducing the underlying stressors wherever possible.

That may involve giving the dog more predictable routines, protected sleep, opportunities to retreat, appropriate exercise, mental enrichment, or more distance from known triggers.

Dogs with fear or anxiety should generally be helped using gradual, reward-based behavior modification rather than repeated forced exposure to whatever frightens them.

Medical problems also need to be addressed.

Pain relief for arthritis, appropriate treatment for gastrointestinal or skin disease, or managing an endocrine disorder may dramatically improve behavior because the physical problem was contributing to the dog's stress load.

Dogs with substantial anxiety may benefit from treatment coordinated between a veterinarian and a suitably qualified behavior professional. In some cases, behavioral medication can be extremely helpful alongside environmental management and behavior modification.

The goal is not to create a dog who never experiences stress.

That would be neither realistic nor desirable.

The goal is a dog who can encounter manageable challenges, recover afterward, sleep well, learn, play, eat normally, and spend most of their life feeling safe.

Arrange a veterinary assessment if your dog's behavior has changed significantly, particularly if the change is sudden.

Signs worth discussing include persistent panting or pacing, major appetite changes, weight loss or gain, repeated vomiting or diarrhea, increased drinking or urination, skin or coat changes, unexplained aggression, reluctance to exercise, sleep disturbance, or difficulty settling.

Behavior is biology.

A dog who suddenly seems “difficult” may actually be uncomfortable, unwell, frightened, or some combination of all three.

A dog's stress response is beautifully designed for short-term survival. It mobilizes energy, sharpens attention, alters circulation, and prepares the body to respond rapidly to danger.

It was never designed to remain switched on indefinitely.

When dogs experience frequent or prolonged stress without enough opportunity to recover, the effects can ripple through the brain, digestive tract, immune system, metabolism, sleep, skin, and behavior.

The science of chronic stress in pet dogs is still evolving, and there is no simple cortisol number that tells us whether a particular dog is coping well. What matters is looking at the whole animal: their health, behavior, environment, sleep, relationships, and ability to recover after challenging experiences.

Sometimes the most valuable question we can ask about an anxious or reactive dog is not, “How do I stop this behavior?”

It is, “What is making their body feel as though it still needs to be on alert?”

Answer that question, and we are much closer to helping the dog rather than simply managing the symptom.