What is considered a dangerous body temperature. How high can a fever go before it becomes a serious health concern. When should you seek medical attention for a high fever. What are the potential complications of an extremely high body temperature.

Defining Normal Body Temperature and Fever

Body temperature naturally fluctuates throughout the day and varies between individuals. However, there are established ranges for what’s considered normal versus feverish.

Normal body temperature typically falls between 36°C (96.8°F) and 37°C (98.6°F). A fever is generally defined as a body temperature of 38°C (100.4°F) or higher. But at what point does a fever become dangerous?

Categories of Fever

• Mild fever: 38°C to 38.9°C (100.4°F to 102°F)
• High fever: 39°C to 39.9°C (102.2°F to 103.8°F)
• Very high fever: 40°C (104°F) or higher

Understanding these categories can help determine the severity of a fever and when medical attention may be necessary.

Recognizing Signs of a Dangerous Fever

While the number on a thermometer is important, it’s not the only factor in determining if a fever is dangerous. Other symptoms and the individual’s overall health play crucial roles.

Symptoms of a Potentially Dangerous Fever

• Severe headache that persists despite pain medication
• Stiff neck
• Sensitivity to light
• Confusion or drowsiness
• Difficulty breathing
• Persistent shivering or chattering teeth
• Fever lasting more than 3 days

These symptoms, especially when combined with a very high fever, may indicate a serious underlying condition requiring immediate medical attention.

The Impact of High Fever on the Body

As body temperature rises, various physiological changes occur. Understanding these effects can help explain why extremely high fevers are concerning.

Effects of Increasing Body Temperature

1. 38°C – 39°C: Mild discomfort, increased metabolism
2. 39°C – 40°C: Moderate to severe discomfort, rapid heart rate
3. 40°C – 41°C: Hallucinations, confusion, seizures possible
4. 41°C – 42°C: Fainting, vomiting, severe headache
5. Above 42°C: Organ failure, brain damage, death possible

Is there a specific temperature at which irreversible damage occurs? While individual responses vary, temperatures above 41.5°C (106.7°F) are generally considered extremely dangerous and can lead to permanent organ damage or death if not treated promptly.

Causes of Dangerously High Fevers

Understanding the potential causes of extremely high fevers can help identify underlying conditions that may require immediate medical intervention.

Common Causes of Very High Fevers

• Severe infections (e.g., sepsis, meningitis)
• Heat stroke
• Certain medications
• Thyroid storm (severe hyperthyroidism)
• Malignant hyperthermia (rare genetic condition)

Are some causes of high fever more dangerous than others? Indeed, causes like sepsis or meningitis can be life-threatening and require immediate medical attention, whereas a high fever from a viral infection may be less concerning if other symptoms are mild.

When to Seek Medical Attention for a Fever

Knowing when to consult a healthcare professional about a fever is crucial for preventing potential complications.

Situations Requiring Immediate Medical Care

• Fever of 40°C (104°F) or higher
• Fever lasting more than 3 days
• Fever accompanied by severe headache, stiff neck, or light sensitivity
• Signs of dehydration (dark urine, dry mouth, sunken eyes)
• Confusion, lethargy, or difficulty waking
• Severe abdominal pain or difficulty breathing
• Recent travel to areas with high risk of infectious diseases

How quickly should you seek medical attention in these situations? For very high fevers or symptoms suggesting meningitis, immediate emergency care is crucial. For other concerning symptoms, contact your healthcare provider within 24 hours.

Managing High Fevers at Home

While dangerous fevers require medical attention, many fevers can be safely managed at home. Understanding proper care techniques can help reduce discomfort and prevent complications.

Home Care Tips for Fever

• Stay hydrated with water, clear broths, or electrolyte solutions
• Rest and avoid strenuous activities
• Use over-the-counter fever reducers like acetaminophen or ibuprofen as directed
• Dress in light, breathable clothing
• Keep the room temperature comfortable, around 21°C (70°F)
• Use a damp cloth to cool the forehead and wrists

Is it necessary to try to “sweat out” a fever? No, this is an outdated and potentially dangerous myth. Focus on keeping comfortable and hydrated instead.

Special Considerations for Fever in Different Populations

The impact and management of fevers can vary significantly between different age groups and health conditions.

Fever in Specific Groups

1. Infants and young children: More prone to high fevers, require closer monitoring
2. Elderly: May not develop high fevers even with serious infections
3. Immunocompromised individuals: At higher risk for severe infections and complications
4. Pregnant women: Fever can potentially affect fetal development

How does the approach to fever management differ for these groups? Generally, these populations require more cautious monitoring and lower thresholds for seeking medical attention. For example, a fever of 38°C (100.4°F) in a newborn warrants immediate medical evaluation.

Complications of Untreated High Fevers

While fever itself is a symptom rather than a disease, prolonged or extremely high fevers can lead to serious complications if left untreated.

Potential Complications of Severe Fever

• Dehydration
• Hallucinations
• Seizures
• Organ damage
• Brain damage (in extreme cases)

Can fever alone cause brain damage? While extremely rare, sustained very high fevers (above 42°C or 107.6°F) can potentially lead to brain damage. However, it’s important to note that such extreme temperatures are usually the result of underlying conditions rather than common illnesses.

Understanding the potential risks associated with high fevers emphasizes the importance of proper monitoring and timely medical intervention when necessary. While most fevers are not dangerous and can be managed at home, recognizing the signs of a potentially serious fever is crucial for preventing complications and ensuring prompt treatment of underlying conditions.

As we continue to explore the complexities of body temperature regulation and fever management, ongoing research provides new insights into how our bodies respond to infections and environmental factors. This knowledge helps healthcare providers develop more effective strategies for diagnosing and treating fever-related conditions, ultimately improving patient outcomes and reducing the risk of dangerous complications.

Remember, while this information provides general guidelines, individual cases may vary. Always consult with a healthcare professional for personalized advice, especially if you have concerns about a fever or other symptoms. By staying informed and attentive to our bodies’ signals, we can better navigate the challenges posed by fevers and maintain our overall health and well-being.

High temperature (fever) in adults

What is a high temperature?

Normal body temperature is different for everyone and changes during the day.

A high temperature is usually considered to be 38C or above. This is sometimes called a fever.

Check if you have a high temperature

You may have a high temperature if:

• your chest or back feel hotter than usual
• you have other symptoms, such as shivering (chills), sweating or warm, red skin (this may be harder to see on black or brown skin)
• a thermometer says your temperature is 38C or above

Important

If you feel hot or shivery, you may have a high temperature even if a thermometer says your temperature is below 38C.

Do I need to take my temperature?

You do not need to take your temperature using a thermometer, but you can if you have one.

Make sure you use it correctly to help get an accurate result. See how to take a temperature.

Treating a high temperature

There are some things you can do to help treat a high temperature.

Do

• get lots of rest

• drink plenty of fluids (water is best) to avoid dehydration – drink enough so your pee is light yellow and clear

• take paracetamol or ibuprofen if you feel uncomfortable

Information:

Try to stay at home and avoid contact with other people until you do not have a high temperature.

Urgent advice: Ask for an urgent GP appointment or get help from NHS 111 if you have:

• a high temperature and you’ve been treating it at home but it’s not getting better or is getting worse

You can call 111 or get help from 111 online.

Causes of a high temperature

Many things can cause a high temperature. It’s not usually a sign of anything serious.

It’s often just caused by your body fighting an infection, such as a cold or flu.

Sometimes it could be a sign of something more serious if your temperature is very high or will not come down.

Information:

Advice for children

This page is for adults. For advice about children, see high temperature (fever) in children.

Page last reviewed: 24 May 2023
Next review due: 24 May 2026

Fever in adults – HSE.ie

This page has general information about fever in adults. If you have a child with a fever, see the page on fever in children.

Normal body temperature is usually between 36 and 36.8 degrees Celsius.

A high temperature or fever is when your body temperature is 38 degrees Celsius or higher. It can be a sign that you are unwell. It usually means you have an infection, such as a cold. But it can also be due to more serious infections, such as COVID-19 (coronavirus).

Prevent the spread of COVID-19

A high temperature of 38 degrees Celsius or above can be a symptom of COVID-19.

Symptoms of COVID-19 and what to do

A fever is usually caused by your body fighting a viral or bacterial infection. It usually lasts around 3 to 5 days. Most people recover from a mild fever with self-care at home.

Symptoms

Your symptoms will depend on the type of fever you have.

Mild fever (38 to 38.9 degrees Celsius)

With a mild fever, you might:

• have flushed cheeks
• feel tired
• be warm to the touch

You will usually be able to carry out normal daily activities.

High fever (39 to 39.9 degrees Celsius)

With a high fever, you might:

• feel hot to the touch
• not feel well enough to go to work
• have aches and pains

Very high fever (40 degrees Celsius or higher)

With a very high fever, you will usually want to stay in bed or be inactive. You will not feel well enough to carry out normal activities. You’ll feel hot to the touch and you may have lost your appetite.

When to see a GP

Most older infants, children and adults do not need medical treatment for a mild fever.

You should contact your GP if you:

• have a very high fever (40 degrees Celsius or higher)
• are still feverish after 3 days of home treatment or seem to be getting sicker
• are shivering or cannot stop shaking, or have chattering teeth, and it does not stop within an hour or so
• have a severe headache that does not get better after taking painkillers
• are having trouble breathing
• are getting confused or are very drowsy
• have travelled overseas recently

Urgent advice: Contact your GP immediately if

you have a fever and notice the following symptoms:

• severe headache
• stiff neck
• sensitivity to light

These symptoms may be a sign of meningitis. This needs urgent medical attention.

Young babies and pregnant women

Babies under 3 months with a fever must see a GP. If your baby is between 3 and 6 months and has a high or very high fever, contact your GP.

Fever in babies and children

If you are pregnant and have a temperature of 38.5 degrees Celsius, or any fever lasting for 3 days or more, see your GP. They need to monitor the effects of the fever on your baby.

Causes of fever

Fever is usually caused by a viral or bacterial infection. Fever is your body’s way of fighting infection. Raising your body temperature helps to kill the virus or bacteria.

Common conditions that can cause fevers include:

• respiratory tract infections
• flu (influenza) and flu-like conditions
• colds
• tummy bugs (gastroenteritis)
• ear infections
• infection of your tonsils (tonsillitis)
• kidney or urinary tract infections

Common childhood illnesses that can cause fevers include:

• chickenpox
• scarlet fever
• rubella (German measles)
• whooping cough
• rheumatic fever

You might have a mild fever after getting a vaccine. Adults should not take paracetamol before or after getting a vaccine. It may make the vaccine less effective.

Treatment

Medicine is not needed for a mild fever. You can use paracetamol if you also have a headache, pain or distress.

Managing a fever yourself

Drink plenty of fluids, especially water (little and often is best). Try to drink 2 to 3 litres in 24 hours while you have a fever. This will reduce the risk of dehydration.

Do

• get plenty of rest

• make sure the room temperature is comfortable – not too hot or too cold

• open a window for ventilation if you can, but avoid draughts

• wear lightweight clothing and use lighter bedding

• use a cool cloth to wash your face, hands and neck

• change bed linen and clothing regularly

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 28 February 2023

Next review due: 28 February 2026

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

What body temperature is considered normal?

Body temperature is individual for each person and depends on different characteristics of the body, however, in some cases, a low or high temperature may indicate serious problems. This was told to Izvestiya by the head of the polyclinic department of the MEDSI Clinical Hospital No. 1 in Otradnoye, a therapist-oncologist Natalia Tolstykh.

According to the specialist, body temperature can be influenced by such indicators as metabolic characteristics, the work of the endocrine glands or the autonomic nervous system. At the same time, for each person during the day, the temperature fluctuates within small limits, remaining in the range from 35.5 to 37.2 degrees for a healthy person.

The temperature may also vary depending on the activity (with high activity, the temperature may rise slightly) and the time of day. Normal daily temperature fluctuations are 0.5–0.7 degrees. When a person falls asleep, all processes in the body slow down and the body temperature drops slightly, getting closer to 35-36 degrees, Tolstykh explained.

“It is important to understand that lower (compared to the population norm) body temperature, that is, less than 35.5 degrees, may be an individual feature of some people, and does not always indicate the presence of diseases. Low body temperature, or the so-called hypothermia (below 35.2 degrees), can be caused by hypothermia, intoxication, problems with the endocrine system (reduced thyroid function – hypothyroidism, or adrenal insufficiency) “- said the oncologist.

Hypothermia also occurs in severe infections among the elderly, with hypothermia. Often the temperature can be lowered within a few days after a person has had an infection – the so-called asthenic trace.

“This is a signal that the body has coped with the infection, but is still weak and there is a risk of getting sick again,” the expert explained.

In addition, exposure to heat and cold, physical activity, consumption of spicy foods and/or heavy meals, and pregnancy (up to 37.4 degrees are common) can cause slight changes in temperature.

“37.1–38 degrees is the so-called subfebrile temperature. It may persist for up to two weeks after infection with fever. In the absence of other symptoms, this condition does not require additional examination and treatment. Quite often, colds occur in an erased form, and the detection of temperature is an accidental finding, ”added Tolstykh.

Speaking of elevated temperature, she emphasized that such a reaction of the body is its response to the introduction of a pathogenic microorganism. With good tolerance, fever up to 38.6 is better not to bring down the intake of antipyretics, since bacteria and viruses reproduce worse at elevated ambient temperatures, the doctor recommended, specifying that this concerns a healthy young body without concomitant pathology.

However, there are exceptions to this general rule. Body temperature should be treated more carefully in some cases.

“Firstly, in the pathology of the cardiovascular system (in particular, coronary heart disease, heart failure), an increase in temperature causes a high load on the heart, an increase in heart rate, therefore, in such cases, the temperature drop threshold can be reduced to 38 degrees. Secondly, with a non-infectious cause of fever (paraneoplastic, that is, tumor diseases, fever, fever in rheumatoid diseases), it makes no sense to withstand high temperatures, ”the specialist said.

According to Tolstoy, children usually tolerate temperatures up to 39 degrees, but the doctor noted that there are people who are sensitive to febrile convulsions, that is, their development when the body temperature rises.

Usually we are talking about a fever above 40 degrees, but convulsions individually can develop at a temperature of 39 degrees or even lower. In such cases, it is important to remember this feature of the child and prevent such an increase in temperature.

“At a temperature of 41 degrees and above, the protein begins to denature everywhere, in fact, the body is boiling – such a temperature is life-threatening,” the expert draws attention. In this case, the temperature must be lowered – antipyretics, cooling with a cold blanket and rubbing will help.

The temperature has risen. What you need to know

37.0 — is this already a disease? When should you take an antipyretic? Can heat kill? Why is it advised to eat less at a temperature? We analyze popular questions

Usually we consider a fever a sign of SARS, influenza or other infectious disease. However, it can also jump after vaccination, although there is no infection in the body. Deviations from the temperature norm have dozens of reasons. To understand why this happens, it is worth learning more about the thermoregulation of our body.

In 1851, the German physician and scientist Karl Wunderlich summarized the results of a million temperature measurements in the armpits of patients and for the first time established the normal limit of 37°C, or 98.6°F. He also put into practice regular measurements of the temperature of patients and argued that fever (fever) is not the disease itself, but its symptom.

However, later studies revised Wunderlich’s estimate and reduced the rate to 36. 6°C. This was due not so much to the scientist’s mistakes as to the improvement in the quality of life. Wunderlich lived in an era when the average life expectancy was 38 years, and many people suffered from chronic infections such as tuberculosis, syphilis and periodontitis. A high level of systemic inflammation in the body could lead to such a norm.

At the same time, the temperature norm also depends on the place of measurement: in the armpit – it is 36.6 ° C, in the anus and vagina – 37.5 ° C; in the mouth – 37.0 ° C. By the way, the axillary method is considered the least accurate, but it has entered hospital practice as the simplest and most hygienic. For example, in the United States at home, a thermometer is placed in the mouth. But not any thermometer is suitable for this, you need a special one.

No. The temperature depends on daily biological cycles (at night and in the morning it is lower than during the day and in the evening), physical and mental activity, emotional state (fear, stress), and ambient temperature. Also, temperature regulation is disturbed by drug and alcohol intoxication. A constant temperature of 37.2 ° C can be in women during the period of ovulation and in pregnant women. Therefore, it is important to measure the temperature, if possible, in a calm, unexcited state.

Without illness or other physiological disturbances, the temperature will not exceed 37.2°C. But then begins what experts call subfebrile (from the Latin febris – fever) temperature – from 37.2 to 37.8 or even 38.0 ° C. Usually she speaks of a sluggish inflammatory process, that the body is fighting infections, and other disorders.

Subfebrile temperature can be distinguished by other signs of the disease – weakness, headache, sweating and body aches.

Yes, but not only. Subfebrile temperature can be observed in hundreds of different conditions. These can be various kinds of infections (for example, this is one of the symptoms of early tuberculosis), poisoning, dental diseases, allergic reactions, latent autoimmune diseases and chronic pathologies.

The temperature within these limits can also increase after receiving a dose of ionizing radiation of 2 to 4 Gy, against the background of hormonal changes in women during menopause. With prolonged or very acute stress, the body can also respond with an increase in temperature – this condition is called psychogenic fever, or thermoneurosis.

It is worth noting that such a temperature in itself does not harm the body. It is simply a tool the body uses to deal with real or imagined threats. For example, an increase in temperature after vaccination is considered a variant of the norm: the body thinks that it is being attacked, and just in case, it “alarms” all defenses.

Infectious agents such as viruses, bacteria and fungi do not live comfortably at certain temperatures. Let’s say 37.0 is already above the average annual temperature of any place on Earth, including the Sahara and the South American tropics. And the higher the column crawls, the worse it is for microorganisms. For example, biologist Arturo Casadevall studied the temperature preferences of 4,082 species of lower fungi. It turned out that less than a third survive at temperatures above 37°C, and only five percent grow at 41°C.

An increase in temperature is an element of non-specific (aimed at a wide range of threats) immunity. The hypothalamus, located at the base of the brain, is responsible for temperature regulation. It responds to signals from biochemical substances floating in the blood, called pyrogens (from other Greek πῦρ – “fire”). At elevated temperatures, metabolic processes are faster, and therefore the action of immune cells is accelerated.

Pyrogens are secreted mainly by cells of the immune system (monocytes, macrophages, T- and B-lymphocytes). When the hypothalamus detects them, it tells the body to generate and retain more heat, causing a fever. In children, the temperature usually rises faster because their immune system is still immature.

It should be said right away that mercury thermometers in Russia have been banned for production since 2020. This is due to the fact that in 2014 Russia signed the Minamata Convention on Mercury, which requires the production, export and import of goods containing mercury and mercury compounds to be stopped.

The advantages of mercury thermometers are their high accuracy (0.1°C error) and reliability. Mercury expands itself due to heat, does not require batteries and microcircuits. But these benefits are outweighed by the health risks posed by mercury vapor from a broken appliance.

Electronic thermometers are more “capricious”, although formally their accuracy is the same. They use a thermal sensor, so they need to be pressed closer to the body – and it is best to measure them orally or rectally. If you do not change the battery in time, the device will begin to “lie”.

But infrared thermometers have lower accuracy. This is due to the fact that the measuring beam passes through the air, which has its own temperature, and this distorts the result (up to 0.2°C). But it gives the result in a matter of seconds, and is convenient when you need to identify a febrile temperature.

A medical thermometer usually ends at 45°C. At 42°C, irreversible decomposition of proteins in the body begins, at 43°C, denaturation (thermal decay) of proteins in brain neurons, which leads to inhibition of brain functions, coma and death.

But even a temperature above 38°C (it is called febrile) is already quite difficult for the body. Blood pressure rises, heart rate rises, the number of decay products of bacteria in the blood increases, which can cause symptoms of poisoning and disrupt brain function (hence hallucinations).

Consequences of prolonged fever may include fainting, heart and kidney failure, dehydration, digestive and nervous system disorders.

As we found out, the temperature helps to fight the disease. Therefore, doctors usually advise taking antipyretics only when the temperature exceeds 38-38.5 ° C. But it depends on the state of the person himself, on how he tolerates the fever. In this case, an overdose of the drug can cause serious damage to the liver, kidneys, gastrointestinal tract, heart and brain.

If the fever is due to hormonal causes, such as hot flashes during menopause or a thyroid disorder (hyperthyroidism), these medicines will not work. In such cases, cooling treatments such as rubbing with a damp towel or bathing in cool water help.

As far back as the 1574 dictionary of John Whizels, it was noted that “fasting is an excellent remedy for fever.” But if the recommendation to drink more fluids has an obvious explanation (replenish fluid balance and remove the breakdown products of pathogens from the body), then what about the advice to eat less?

On the one hand, in order to maintain a high temperature, the body needs additional energy, which it can get from food. Fasting also creates additional stress. On the other hand, overeating and eating too spicy, unusual, unfamiliar foods can be harmful. The body may misinterpret certain substances as allergens and provoke a reaction.

Such a method exists. For example, in the middle of the 20th century, the German physician von Ardenne began to use it on cancer patients as a means of “last hope”. The fact is that cancer cells die at temperatures close to 42°C. Von Ardenne was able to heat patients up to 41.8°C. True, no more than 17% of them survived, but they were cured.

The “water” method was used for heating. The patient was placed in a special bath and with the help of water-jet devices placed over the patient, and poured over with heated water. Body temperature should have risen to 42-43°C. This procedure lasted about 6 hours under general anesthesia. The head was cooled with a special helmet. Later in the USSR, the idea of ​​heating with microwaves was developed.

Hyperthermia can help treat cancers that are difficult to operate on (eg, brain, mouth, and neck tumors). Heated tissues are more sensitive to ionizing radiation, which increases the effectiveness of radiotherapy. The problem is that it is not yet possible to concentrate the source of thermal radiation exactly at the site of the tumor without affecting other tissues.

Nevertheless, in recent years, the interest in therapeutic hyperthermia among scientists has been growing due to the development of new technologies.