What this means
A sudden or new change in behaviour is a reason to have a vet rule out pain and illness first. Dogs hide pain, and a growl, a flinch or a bite is often the only way of saying "that hurts, do not touch". That is how a loving, always gentle dog with sore joints, teeth or back can react where it never did before.
It helps to note exactly when the change appears: whether it happens when the dog is stroked in a certain place, lifted off the floor, touched on the ears, approached near its bowl, or handled for grooming. Also note whether it began suddenly or grew gradually, and whether appetite, sleep, movement or thirst changed alongside it. These observations help a vet far more than a general description.
Aggression can also come from fear or tension, and from changes in the nervous system or hormones. Here we describe only what an owner can observe and write down. Until the cause is known, it is sensible, for safety, to give the dog space and to keep children from being alone with it.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Pain
Pain in the joints, back, ears or belly can make a dog defend the sore spot. The reaction often appears only when it is touched or lifted.
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Tooth and mouth pain
Aching teeth or gums can cause irritability, reluctance to have the muzzle touched, and a change in how the dog eats.
About the condition: Dental and gum disease -
Fear or anxiety
A frightened dog that cannot get away may growl or bite. Flattened ears, a lowered tail or backing off often go with it.
About the condition: Anxiety -
Changes in the nervous system
Seizures, their aftermath or other brain disorders can cause confusion and unexpected reactions the dog cannot control.
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Hormonal disorders
Some hormone problems, such as an underactive thyroid, are linked with changes in mood and behaviour along with lethargy or weight change.
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Guarding an item or a spot
A dog may growl near its bowl, a toy or its resting place. If this appeared suddenly, it is worth finding out whether pain or illness lies behind it.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the aggression began suddenly or grew gradually
- Where and when exactly your dog growls or snaps
- Whether it avoids being touched on any part of the body
- Whether appetite, thirst, sleep or movement have changed
- Whether it has started limping or avoids jumping and stairs
- Whether it seems confused, wobbly or has a vacant look
When to book a routine visit
Book a visit as soon as your dog changes suddenly, even if it happened only once. Tell the clinic in advance that your dog may bite, and note when and where it happens.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Anxiety General health Anxiety is a state in which a dog feels tension and fear constantly or far too strongly, even when there is no real danger. It can be set off by being left alone, loud noises, new surroundings or strangers, and long-lasting anxiety wears down both the dog and the whole household. It helps to understand that this behaviour is not stubbornness or disobedience but a sign that the dog is struggling.
- Arthritis Bones and joints Arthritis is inflammation of the joints in which the cartilage gradually wears down, leaving the joint stiff and painful. It can develop with age, after an injury or because of joints that did not form properly. Ongoing pain limits how freely and comfortably a dog moves, so changes are worth showing to a vet.
- Dental and gum disease Digestion and liver Dental and gum disease starts with plaque that hardens over time into tartar, and the bacteria multiplying beneath it cause inflammation of the gums. Left alone, the inflammation can damage the tissues and bone that hold the tooth in place, so teeth loosen and fall out. A sore mouth troubles a dog every day, and infection in the mouth can affect other organs too.
- Epilepsy and seizures Nerves and muscles A seizure is a sudden disturbance of the brain's electrical activity that can make a dog twitch uncontrollably, fall over or briefly lose consciousness. When seizures keep coming back and no other clear cause is found, this is called epilepsy, but seizures can also be caused by poisoning, other illnesses or head injuries. A seizure can be life-threatening, so the dog needs a vet immediately.
- Hypothyroidism Hormones and metabolism Hypothyroidism is a condition in which the thyroid gland produces too little of the hormones that regulate metabolism. Because these hormones affect almost the whole body, a shortage gradually slows many of its processes. The changes come on slowly, so they are easy to mistake for ageing or simple laziness.
- Rabies Infections Rabies is a viral disease of the nervous system that a dog catches when it is bitten by an infected animal. It is dangerous to animals and to people alike. If your dog has been bitten by a wild or unknown animal, or its behaviour has changed so suddenly that you suspect rabies, phone a vet immediately.
Body systems: General health Bones and joints Digestion and liver Nerves and muscles Hormones and metabolism Infections