Fever in dogs: signs, taking the temperature, causes and when to see a vet

A fever in a dog is not a disease in itself, but a sign that something worrying is going on in the body. It may accompany an infection, an inflammatory process, a tick-borne disease, an immune disorder and sometimes other, less obvious health problems. So the first thing that matters is not only noticing that the temperature has risen, but also working out whether you are dealing with a genuine fever or rather with an overheated body, that is, hyperthermia. In this article we show how to assess the situation sensibly, how to interpret your dog’s temperature and when it is not worth waiting before contacting the practice.

What is a fever in a dog, and at what temperature does it become a problem?

What is a normal temperature for a dog?

A dog’s normal body temperature usually falls somewhere between about 37.5 and 39.2°C. That is a fairly wide range, and it is worth remembering that a single reading should not be interpreted in isolation from the whole clinical picture. The dog’s age and size matter, as do the stress level during the examination, activity just before the reading and general health. In some dogs the temperature may rise briefly after strong excitement or exercise, which does not automatically mean a fever in the clinical sense. The number on the thermometer is important, then, but it always has to be read together with the animal’s symptoms and behaviour.

When does it count as a fever?

In practice a simple division works well. Up to about 39.2°C the temperature is usually still within the physiological range. A reading approaching 39.5°C already calls for attention, especially if the dog is subdued, off its food or behaving differently from usual. A temperature above 39.5–39.7°C is most often regarded as a fever, and 40°C or more calls for a prompt veterinary consultation, particularly if other symptoms are present. A very high temperature, especially around 41°C or above, is an emergency and needs urgent assessment, as it may point to a severe infection, marked inflammation or an overheated body.

It is also worth remembering that not every raised temperature means the same thing. A dog reading 39.6°C who is only slightly subdued is a completely different situation from a dog at 40.5°C with rapid breathing, dehydration and trouble keeping its balance. That is why two things matter at once in any assessment at home: the temperature reading and the dog’s general condition. The higher the temperature and the worse the dog feels, the less room there is for waiting “until tomorrow”.

Fever and hyperthermia are not the same thing

This is one of the most important distinctions in the whole subject. Fever is a response the body itself regulates: under the influence of a disease process, the immune system resets the internal thermostat to a higher level. This can accompany infections, inflammatory conditions, immune-mediated disease or cancer. Hyperthermia, by contrast, is an uncontrolled rise in body temperature that does not come from a shifted set point but from the body overheating — in hot weather, for instance, after being shut in a hot car, after very intense exercise or during heatstroke. These are two different mechanisms, which is why they call for slightly different clinical thinking.

In practice this matters enormously. With a fever, the key thing is to look for the source of the inflammation or infection. With hyperthermia, the problem is that the body cannot shed heat fast enough and the temperature keeps rising despite attempts to cool it. In an overheated dog you are more likely to see frantic panting, extreme agitation or, conversely, weakness, drooling, neurological signs and rapid deterioration. If the dog has been exposed to high ambient temperatures or heavy exercise, a very high reading should immediately raise the possibility of hyperthermia and heatstroke, not just an “ordinary fever”.

What are the signs of fever in a dog?

The signs owners most often notice at home

In a dog with a fever, changes in behaviour are usually the first thing to catch the eye. The animal becomes more listless, less willing to move, lies down sooner, visibly loses energy and avoids activities it normally enjoys. Appetite often drops or the dog refuses food altogether, sometimes even favourite treats. Some dogs shiver, tremble, breathe faster, become sleepy or restless. If the underlying disease involves the digestive or respiratory system, vomiting, diarrhoea, coughing or other signs may appear as well, depending on the cause.

It is worth watching not only for the “big” signs but also for subtler ones. The dog may sleep more, hide away somewhere quiet, be reluctant to get up, seem “dimmed” or react differently to being touched. Sometimes the owner simply feels that the animal “isn’t itself” — and very often that observation turns out to matter. Fever on its own does not produce one perfectly characteristic picture, so it is best to look at the dog as a whole: temperature, behaviour, appetite, thirst and breathing rate.

Do a dry nose and warm ears mean anything?

This is one of the most frequently repeated home “tests”, but let us be clear: a dry nose and warm ears are not a reliable way to detect a fever. They can accompany feeling unwell, dehydration, excitement, exercise or simply a change in the surroundings. Many owners do notice that their dog’s ears feel warmer or its nose drier when it has a fever, but that sign alone cannot tell you whether the temperature really is raised. The only sensible confirmation is a reading from a thermometer.

This matters, too, because relying on the nose or the ears alone can lull you into a false sense of security or, conversely, raise the alarm for nothing. A dog can have a dry nose and no fever, and it can have a fever without a noticeably “hot” face. So if your dog seems unwell, subdued or clearly out of character, it is better not to guess but to take its temperature and assess the whole situation more objectively.

Warning signs you should not wait out

There are situations in which it makes no sense to watch the dog for another few hours and hope it “sorts itself out”. You need to contact the practice quickly if the raised temperature comes with very rapid or laboured breathing, marked weakness, dehydration, seizures, an unsteady gait, neurological signs, fainting, collapse, or mucous membranes that are very pale or, conversely, dark red. The situation is especially urgent if heatstroke is suspected: the dog has been in the sun, in a hot car, exercising hard or in a stuffy room, and suddenly becomes extremely weak, pants heavily, drools or stops responding normally.

Nor should you wait if the dog is very young, very old, chronically ill, or has additional signs alongside the fever such as persistent vomiting, diarrhoea, severe pain, an inability to drink or a clear loss of contact with its surroundings. In such cases it is not only the temperature itself that matters, but how fast the animal’s condition is deteriorating. The more severe the clinical picture, the more prompt diagnostic work counts, rather than monitoring at home.

How to take a dog’s temperature properly

Why a rectal thermometer is still the most reliable

If you genuinely want to know whether your dog has a fever, the most reliable method remains taking the temperature rectally. Veterinary reference ranges are based on exactly this kind of reading, which is why it has the greatest practical value. In a healthy dog the normal rectal temperature usually lies between about 37.5 and 39.2°C, but a single reading must always be interpreted alongside the symptoms, the patient’s stress level and its general condition.

Many owners try to judge temperature by the nose, the ears or the dog’s behaviour, but this can be misleading. A dry nose does not automatically mean a fever, and warm ears are no reliable substitute for a measurement. So if your dog seems subdued, weaker than usual or clearly “not itself”, it is better not to guess but to take the temperature as objectively as you can.

Step by step

A digital thermometer is best, ideally one kept for the animal alone. An ordinary electronic thermometer from the chemist will do, as long as it works properly, is clean and is used only for the dog. It is also worth having a little petroleum jelly, lubricant or another safe lubricating product to hand, plus a tissue or swab to clean the device afterwards.

The procedure itself should never be rushed or forced. Ideally the dog will stand calmly or lie on its side, with a second person holding it gently if it is restless. Lubricate the tip of the thermometer lightly, then calmly lift the tail and insert the thermometer into the rectum very carefully. In most dogs a shallow insertion is enough — being gentle and causing no pain matters far more than going deep. After a few moments, once the device has finished, remove the thermometer, read the result and disinfect it thoroughly.

If your dog is already anxious about being touched in that area, do not turn the whole thing into a wrestling match. A reading taken in a state of agitation is not only unpleasant but also unreliable, because strong stress and excitement can affect the result. In practice what counts is not just the figure on the display, but whether you were able to obtain it in conditions that were as calm and safe for the dog as possible.

When it is better not to do it yourself

There are situations in which even a technically correct method is a poor idea at home. If the dog is aggressive, in a great deal of pain, struggling to breathe, extremely weak or unsteady on its feet, what matters most is getting to the practice quickly, not fighting for a reading at home. The same applies if you suspect an injury, severe pain around the pelvis or anus, or if merely handling the dog triggers a panicked reaction.

The rule is simple: if the reading can be taken calmly and safely, take it, because the result helps in assessing the situation. But if the attempt itself means extra stress or a risk of making the dog worse, it is wiser to leave the assessment to the veterinary team. At moments like these, time and patient safety count for more than accuracy at home.

Where does fever in dogs come from? The most common causes

Viral, bacterial and fungal infections

Fever in a dog most often appears when the body is responding to an infection. The source may be viral, bacterial, fungal or parasitic. In clinical practice the vet will consider, among other things, respiratory infections, diseases of the digestive tract, infections of the skin and soft tissues, and also systemic diseases that initially produce only non-specific signs such as weakness, reluctance to eat and a raised temperature. In some cases the fever is the first clear signal that a problem is developing and needs further investigation.

The infectious causes also include more serious diseases, such as parvovirus in puppies or certain tick-borne infections. The point is not to link every rise in temperature to the worst possible scenario, but to be aware that fever rarely appears “for no reason”. Even if the signs seem mild at first, the immune system is usually responding to something specific: an infection, tissue damage or an inflammatory process.

Inflammation of organs and tissues

Not every fever in a dog comes directly from an infection. A high temperature can also accompany inflammation developing in internal organs or tissues — in the lungs, pancreas, uterus, joints and digestive tract, for instance, but also abscesses, infected wounds and deeper inflammatory changes that the owner cannot see with the naked eye. In such cases the dog may have a fever, obvious discomfort, a poorer appetite and weakness, but no single easily spotted sign that points straight to the source of the problem.

This is precisely why “the dog has a fever” tells you very little about the cause on its own. In one patient the source will be pneumonia, in another an abscess following an injury, in one bitch a pyometra, and in yet another an acute inflammatory process in the abdomen. For the owner, then, what matters is less a guess made at home than recognising quickly that a raised temperature reflects a real health problem whose source needs to be identified.

Tick-borne and other infectious diseases

Owners very often type questions such as “fever in a dog after a tick bite” or “does a dog run a temperature with Lyme disease” into a search engine. And with good reason, because tick-borne diseases really can cause fever, weakness, loss of appetite, lameness, pain and a general decline in wellbeing. It is worth remembering, though, that “after a tick” does not automatically mean one particular disease. The clinical picture depends on the pathogen involved and on how the dog’s body responds to it.

The same is true of leptospirosis and other systemic infections: fever may be one of the first signs, but it is rarely the only one. So if your dog has been exposed to ticks, lives in an area where tick-borne disease is more common, or develops lethargy, pain, lameness, vomiting or kidney problems alongside the fever, proper diagnostic work is needed rather than guesswork at home.

Rarer causes that still matter

There are also cases in which the fever stems neither from a typical infection nor from obvious inflammation. Sometimes the body responds with a rise in temperature to a medicine, a vaccination, an immune process or a tumour. In some patients a fever may also follow surgery, though then it is especially important to establish whether this is a normal post-operative response or a developing complication. It is in these less obvious cases that a vet may consider what is known as a fever of unknown origin, or FUO.

FUO is not a diagnosis of the cause but a name for the clinical situation in which a dog has a persistent fever and the source of the problem is not immediately apparent on basic assessment. That is significant, because it shows that even with a thorough examination and a sensible diagnostic plan, the answer does not always come at once. Such cases may call for blood and urine tests, imaging, infectious disease testing and further step-by-step investigation.

Can stress raise the temperature?

Yes, stress can raise a dog’s body temperature briefly. This happens above all during strong excitement, on a journey, at the practice or in any situation where the dog is very anxious and tense. Such a rise is usually moderate, though, and should be interpreted with great care. Stress does not explain everything, especially if the dog looks unwell, has other signs or the temperature is clearly high.

The important thing is not to use stress as a convenient explanation for every abnormality. A dog may indeed push its temperature up in the consulting room out of nerves, but a very high fever, marked weakness, vomiting, dehydration or breathing difficulties call for a proper clinical assessment. In other words: stress may influence the reading, but it should not lull you into complacency where the signs suggest a real health problem. 

What to do when your dog has a fever

First steps at home

If you suspect your dog has a fever, try first to assess the situation calmly rather than acting on emotion. The most important thing is to take the temperature, and then to look at the whole clinical picture: is the dog subdued, is it drinking, is it breathing normally, does it have an appetite, is there vomiting, diarrhoea or obvious pain? The figure on the thermometer counts, but how the animal looks and behaves at that moment counts just as much. A temperature above roughly 39.5–39.7°C is already regarded as a fever, and the higher the reading and the worse the dog feels, the more urgent the consultation becomes.

At home, the priorities are peace and quiet, a chance to rest and constant access to fresh water. There is no point in tiring the dog out with walks, play or extra stimulation when its body is clearly fighting a health problem. It is also worth watching the accompanying signs: is the dog drinking less than usual, is it passing urine, is its breathing speeding up, is there any trembling, apathy or reduced responsiveness? This is exactly the sort of information that often proves very useful when you speak to the veterinarian.

What not to do

This is one of the most important sections in the whole article. If your dog has a fever, do not give human fever or pain medicines on your own initiative. Ibuprofen, naproxen, aspirin and paracetamol/acetaminophen should not be given to a dog without a clear instruction from a veterinarian, because they can cause severe adverse effects, including damage to the digestive tract, kidneys and liver, or clotting disorders. That includes those moments when an owner just wants to “bring the temperature down a bit”. The impulse is understandable, but the method is wrong and can end in a far bigger problem than the fever itself.

Nor should you cool the dog abruptly with ice-cold water or force the temperature down with home remedies without knowing what you are actually dealing with. Where overheating or heatstroke is suspected in particular, the advice is prompt, safe cooling with cool — not ice-cold — water and contacting the practice as quickly as possible, because over-aggressive measures can do harm, and cooling is no substitute for veterinary care. Nor is it worth putting off the visit if the dog is clearly subdued, has a high temperature or is getting worse from hour to hour.

When to see a vet urgently

An urgent consultation is needed when the dog’s temperature exceeds the fever threshold and other worrying signs are present at the same time, or when the temperature itself is very high. More important than a single figure is whether the fever persists, whether the dog stops eating and drinking, whether it becomes markedly weak or dehydrated, or has vomiting, diarrhoea, tremors, rapid breathing or difficulty breathing. A fever above 39.7°C that persists for several days with no obvious cause already falls into the territory of FUO — fever of unknown origin — and calls for investigation.

Particular caution is needed with puppies, older dogs and animals with chronic illness. These groups usually have less reserve, so dehydration, weakness or a flare-up of an existing condition come on faster. Immediate assessment is also needed where heatstroke is suspected: heavy panting, drooling, weakness, vomiting, diarrhoea, an unsteady gait, neurological signs, collapse or exposure to high ambient temperatures are all signals that should not be left to wait.

How does a vet find the cause of a fever in a dog?

History and clinical examination

The diagnostic process starts with simple but very important things. The veterinarian will usually ask when the signs began, how high the temperature was, whether the dog has been exposed to ticks, been vaccinated recently, travelled, had surgery, suffered an injury or is on any medication. Appetite matters too, as does the presence of vomiting, diarrhoea, coughing, lameness, pain, breathing problems or changes in behaviour. In many cases a well-taken history narrows the list of possible causes far more than the owner expects at the start of the visit.

The clinical examination allows the vet to assess the dog’s general condition, hydration, respiratory and circulatory function, mucous membranes, abdomen, lymph nodes, joints and skin, and to look for painful areas. Fever can be a sign of very different problems, so the vet is not looking at “the temperature” alone but at the whole clinical context. In one dog the clue will be a cough and abnormal lung sounds, in another abdominal pain, and in a third lameness after exposure to ticks.

Tests that may be needed

Depending on the suspected cause, the vet may recommend a full blood count, biochemistry, urinalysis, tests for particular infections and imaging such as X-rays or ultrasound. Where a fever persists with no obvious source, the diagnostic plan tends to be built up gradually, step by step. For FUO cases, the veterinary literature stresses exactly this systematic approach: from history and clinical examination, through basic laboratory tests, to more advanced imaging or additional testing if the first results provide no answer.

This matters from a practical point of view as well. Owners often expect one quick answer to the question “where has this fever come from?”, but in some cases the diagnosis does not emerge from a single test. Sometimes the source is a bacterial infection, sometimes a tick-borne disease, sometimes an immune process, and sometimes a tumour or inflammation hidden deeper in the body. That is why investigating a fever in a dog is often more of a process than a single test.

Why the temperature itself is not what gets treated

Fever is a sign, not a diagnosis. Medically, then, the priority is not simply “bringing the temperature down” but establishing why it rose. One dog will need treatment for inflammation, another antibiotics, a third intensive fluid therapy, and another hospitalisation and further investigation. Focusing solely on the number on the thermometer can therefore draw attention away from the real problem.

Treating fever in dogs: what it involves

Treatment depends on the cause

There is no single universal protocol for treating fever in dogs, because the temperature rises for many different reasons. If the source is an infection, treatment will look different from a tick-borne disease, overheating, dehydration, a post-operative problem or an immune process. Sometimes outpatient treatment and follow-up are enough, but more severe cases call for intravenous fluids, monitoring of vital parameters, anti-inflammatory drugs, pain relief and occasionally hospitalisation.

With hyperthermia and heatstroke, prompt, safe cooling and supportive care are crucial, because here the problem is not just the high temperature but also the risk of organ damage. With infectious or inflammatory disease, on the other hand, the aim is to bring the underlying process under control. This is why two dogs with a similar temperature reading may need entirely different management.

Does a fever always have to be brought down?

Not always. In veterinary practice, treating the cause behind the temperature matters more than mechanically lowering it. The vet judges whether medication, fluids, cooling, hospitalisation or further investigation are needed. Fever is part of the body’s response to disease, so not every fever needs to be suppressed aggressively. A moderately raised temperature in a dog whose general condition is good is one thing; a very high temperature with weakness, dehydration or suspected heatstroke is quite another.

Prognosis: what it depends on

The prognosis depends on several things at once: how high the temperature is, how long it persists, the cause, the dog’s age and any concurrent disease. How quickly investigation and treatment were started also makes a considerable difference. In a dog with a short-lived fever and a mild infection, the situation can be brought under control relatively quickly. In a dog with a severe systemic infection, heatstroke, immune-mediated disease or cancer, the outlook depends on a far broader clinical picture and on the response to treatment.

FAQ

At what temperature does a dog have a fever?
A dog’s normal rectal temperature usually lies between about 37.5 and 39.2°C. A reading above 39.5–39.7°C is most often regarded as a fever, especially if the dog is subdued, off its food or showing other signs. A very high temperature, particularly around 41°C or above, needs urgent veterinary assessment.

Does a dry nose mean a dog has a fever?
No. A dry nose can appear after sleep, with dehydration, excitement or simply feeling unwell, but on its own it is not a reliable indicator of fever. Only a temperature reading can confirm it.

How can I take my dog’s temperature without stressing it?
A rectal thermometer is the most reliable, used calmly and gently and, if the dog is restless, ideally with a second person helping. Use a digital thermometer, lubricate the tip lightly and never force anything. If the dog becomes very stressed, is in a lot of pain, is aggressive or extremely weak, it is better not to fight for a reading at home and to contact the practice instead.

Can a dog have a fever after vaccination?
Yes, a temporary reaction can follow a vaccination, including feeling under the weather and a rise in temperature. If the fever is high, persists, worsens or comes with other marked signs, however, you should contact your veterinarian.

Can stress raise a dog’s temperature?
Yes, stress can raise body temperature briefly, especially during strong excitement, on a journey or at the practice. Such a rise is usually moderate and should not automatically be used to explain a very high temperature or clear signs of illness.

Can I give my dog paracetamol or ibuprofen?
Not without a clear instruction from a veterinarian. Medicines intended for people, including ibuprofen, naproxen, aspirin and paracetamol/acetaminophen, can be dangerous for dogs and cause severe adverse effects.

When is a fever in a dog an emergency?
When the temperature is very high, or when it comes with signs such as breathing difficulty, very rapid breathing, weakness, dehydration, vomiting, diarrhoea, seizures, an unsteady gait, collapse or other neurological signs. Especially prompt action is needed where heatstroke is suspected, and in puppies, older dogs and animals with chronic illness.

Are fever and overheating the same thing?
No. Fever is a regulated response of the body to a disease process, whereas hyperthermia means overheating — in hot weather, after exercise or in the course of heatstroke, for instance. The distinction matters, because the underlying mechanism and how urgently you must act may differ.

Does every fever in a dog mean an infection?
Not always. Fever can accompany an infection, but also inflammation, tick-borne disease, an immune problem, a reaction to a medicine, the period after surgery or other systemic illnesses. The temperature alone therefore does not yet tell you what is causing the problem.

Does a fever always have to be brought down?
Not always. The priority is to establish why the temperature rose. Sometimes anti-inflammatory treatment is needed, sometimes fluid therapy, sometimes further investigation or hospitalisation. Lowering the temperature without knowing the cause does not solve the problem.

When is a fever called a fever of unknown origin (FUO)?
Most often when the temperature exceeds 39.7°C and persists for several days while the cause is not obvious from the history and clinical examination. Such a case usually calls for further step-by-step investigation.

Should a dog with a fever go for its usual walk?
If your dog has a raised temperature and looks unwell, it is better to keep activity to a minimum and provide rest, water and observation. There is no point in tiring it out with a long walk, running or play until you know what is causing the problem. This is especially important if there is a risk of overheating or the dog is clearly weak.