Causes & reasons for a restless or stressed dog [Part 3]

When a dog suddenly barks “out of nowhere,” becomes highly aroused on the Leash, or can no longer settle at home, we humans instinctively look for one single reason. The trigger. The moment when things tipped over. In our work, however, we see every day that this one reason almost never exists. stress in dogs is, in the vast majority of cases, a summation phenomenon: many small stressors come together until the nervous system has no reserve left. We call this principle trigger stacking, and it is the central perspective for Part 3 of our series.

In Part 1, we clarified the basics – what stress actually is and how we can recognize it. Part 2 focused on the physiological inside view – what happens in the body. In this part, we now look at the causes: What triggers are there, how do they interact, and why do we often completely miss the most important ones?

Why one trigger is almost never the one trigger

Research into stress in dogs has developed significantly in recent years. Beerda and colleagues showed as early as the late 1990s that stress manifestations in dogs are multidimensional – meaning they occur simultaneously on hormonal, physical, and behavior-related levels. More recent work, including by Hekman and colleagues, confirms this multidimensionality: stress responses arise from the interaction of different sources of stimuli, not from isolated individual stimuli.

For us in everyday life, this means a shift in perspective: If Amalia reacts especially sensitively to a sound on a particular day, we do not first ask, “What was that sound?” but rather, “What happened in the 24 to 72 hours before?” Poor sleep, a demanding visit to the vet, many close encounters, high pressure of expectations – each of these elements can be inconspicuous on its own. In combination, they lower the threshold at which visible behavior appears.

The threshold model – simply explained

We like to use an image for this: Imagine a barrel. Every small stimulus – a doorbell, an encounter, a loud door – is a drop. A well-regulated, rested dog has an empty barrel; many drops can fall in without anything overflowing. A chronically stressed dog starts the day with the barrel already three-quarters full. Then a single additional drop is enough – a dog on the other side of the street – and the barrel tips over. What we see is the escalation. What we do not see are the 50 drops before it.

Exactly this shift is relevant for training: The moment of escalation is not the lever; the lever is everything that filled the barrel beforehand.

The five main categories of triggers

For trigger work to be structured at all, we sort sources of stress into five broad categories. This classification aligns with what we know from applied behavior research – including the work of Casey and colleagues on context-specific stress factors.

1. Environmental stimuli

This includes everything that comes in through the senses: noise, visual stimulus density, smells, vibrations, light, temperature. City dogs have a different stress profile here than dogs in rural areas. Sounds – especially unpredictable ones – are among the best-studied stressors. For Amalia, certain deep, sudden sounds are still among the stimuli we actively manage. She came to us at six months old, with a largely unknown history, and exactly this class of sounds showed very clearly in the first few weeks that there was a learning history behind it.

2. Social stimuli

Encounters with other dogs, with unfamiliar people, social conflicts within the household, but also separation all belong here. In 2021, Lenkei and colleagues published an extensive paper in Scientific Reports on separation-related behavior, showing that what we colloquially call “separation anxiety” is actually an umbrella term for very different patterns – including fear-based reactions, but also frustration and physical restlessness. This has direct consequences for training work, because frustration requires a different intervention than fear.

3. Medical factors – especially pain

This area is dramatically underestimated in everyday life. In 2020, Mills and colleagues published a widely cited paper in “Animals” on pain and problem behavior. One of its central statements: In a relevant proportion of cases involving behavior abnormalities – the authors speak of an order of magnitude of around one third – pain is involved, without it initially being noticed by dog owners or often even by veterinarians. Musculoskeletal problems, abdominal pain, skin irritations, tooth pain – they all lower the stimulus threshold and often change behavior subtly before clinical signs become visible.

4. Learning history

What a dog has learned in life – through classical conditioning, through their own experiences, through repetition – shapes which stimuli are triggers for them in the first place. A dog who has repeatedly been harassed by off-leash dogs evaluates stimuli differently from a dog who has never had that experience. This is not a question of character, but of neurobiology: The limbic system stores relevant experiences with high priority.

5. Dog owner state

This point is often dismissed as soft or esoteric – but it is now very well documented. In 2019, Sundman and colleagues published a paper in Scientific Reports showing that long-term cortisol levels in dogs and dog owners synchronize. Not the other way around, as one might intuitively assume – rather, the dog primarily follows the human. This matches our practical experience: On days when we ourselves move through the day tense and strained, our dogs read that too. Dog owner state is therefore not a moral accusation, but a real, measurable trigger factor.

Trigger stacking: When small things add up

When we consider these five categories together, it becomes clear why trigger stacking is so central. Five small stressors over three days can physiologically create significantly more stress than one single major trigger that subsides afterward. This is exactly what McPeake and colleagues described in 2021 in a paper on frustration in dogs: Using behavioral and physiological measurements, the authors show that cumulative stress – meaning repeated stimuli occurring in close succession – produces different response patterns than isolated individual stimuli.

For us, this is the scientific underpinning of what we observe every day: A dog who slept poorly in the morning, then had two close encounters on the walk, then went to the vet, and later had visitors in the house in the afternoon – that dog is not being “impudent” in the evening if they no longer want to respond. They are physiologically depleted.

Separation anxiety, separation stress, frustration – subtle differences

Within social stimuli, it is worth taking a closer look at what is colloquially grouped together as “separation anxiety.” Lenkei and colleagues distinguish several subgroups here, and this distinction is enormously important in everyday life. A dog who shows pronounced fear during separation – such as salivating, trembling, panic behavior – needs a different approach than a dog who is primarily frustrated because they are not allowed to come along, or than a dog who shows physical restlessness because they have never learned to settle alone. We therefore prefer to speak of a “separation-related issue” as a generic umbrella term and then ask precisely: Is it fear, frustration, insufficient self-regulation – or a mix?

Trigger detective work in everyday life

From all of this, a very practical consequence follows for us: Trigger work is detective work. No one can see from the outside what is in a dog’s barrel. We cannot either, even though we work with dogs every day. That is why we work – and also recommend to our course participants – with a structured approach.

1. A simple stress diary

Over two to four weeks, we note down brief, honest data: When was the dog restless, what happened in the 24 hours before, how was their sleep, were there any physical abnormalities, what was our own day like. Three to five bullet points per entry are enough. We also use this again and again with Vito when we feel that something is “not right,” but no clear trigger is visible.

2. Look for patterns, not individual cases

After two to three weeks, we look at the overall picture. What repeats itself? Which days were especially difficult, which were uneventful? Often, this is when you see for the first time: It is never single events, but clusters. Days with three or four stimulus factors are the critical ones, not the days with one dramatic individual stimulus.

3. Form hypotheses, do not look for someone to blame

We deliberately formulate hypotheses, not diagnoses. “It could be that sleep is the most important factor” – and then we change exactly this one factor for one week and observe. This one-thing-at-a-time logic is slower than broad changes, but it allows us to see what actually has an effect.

4. Do not forget medical assessment

We repeat this deliberately because it is overlooked so often: If behavior changes or does not improve for a long time, a thorough veterinary assessment is part of the process – ideally including an orthopedic evaluation. This is not trainers advertising against veterinarians, but the direct consequence of Mills 2020. Dogs in pain cannot be trained out of it – they need treatment first.

What research has not yet answered clearly

We also want to be transparent here about where science does not yet have definitive answers. The exact weighting of the five trigger categories in an individual case is individual – there is no formula for how much sleep deficit “equals” how many encounters. The exact amount of time a dog needs for physiological recovery after a peak stress event also varies greatly between individuals. Initial indications point to time frames of 24 to 72 hours, but this has not yet been conclusively investigated. And for many interventions used in everyday training, long-term data on effectiveness are lacking. This is exactly why we at Vitomalia say transparently: We work with the current state of knowledge, and it will continue to change.

Our Vitomalia conclusion

If there is one thing we have taken from years of working with stressed and reactive dogs – including our own, Vito and Amalia – it is this sentence: The final trigger is almost never the explanation. What we see in the moment of escalation is the end of a chain, not its beginning. That is precisely why, for us, trigger work is always also stress management – sleep, breaks, distance, stimulus density, medical clarification, dog owner state. Everything before the actual “problem moment.”

When you understand trigger stacking, you stop blaming dogs for symptoms and start shaping the system behind them. That is slower, but fairer – and based on everything research shows, the only path that is truly sustainable.