Fever is one of the most common symptoms seen in both adults and children. It may occur with something as simple as a short viral infection, but it can also be a warning sign of a more serious illness.
Although people often worry about the number displayed on the thermometer, the temperature alone does not tell us how serious an illness is. Age, associated symptoms, hydration, breathing, alertness, duration of illness and underlying medical conditions are equally important.
A body temperature of 38°C (100.4°F) or higher is generally considered a fever, although normal temperature varies between individuals and also changes during the day.
This guide explains what fever is, why it happens, its common causes, how to measure temperature correctly, what you can safely do at home, when medicines may be useful, and the warning signs that should never be ignored.
What Is Fever?
Fever, medically known as pyrexia, is a temporary rise in body temperature caused by an increase in the body's temperature set point.
The body's temperature is regulated mainly by an area in the brain called the hypothalamus. During fever, the hypothalamus temporarily sets the target temperature higher than normal.
This is usually part of the immune system's response to infection.
For example, if the body's usual temperature is around 37°C and the hypothalamus temporarily raises the target to 39°C, the body begins trying to reach that higher temperature.
This explains why someone can actually be developing a fever while simultaneously feeling extremely cold.
Why Do We Get Chills During Fever?
One of the most confusing features of fever is that people often feel cold and shivery even though their body temperature is rising.
When the hypothalamus raises the body's temperature set point, the body believes its current temperature is too low.
It responds by trying to generate and conserve heat.
This can cause:
Shivering
Chills
Cold hands and feet
Goosebumps
A desire to cover yourself with blankets
Shivering produces heat through rapid muscle activity.
Once the body reaches the new temperature set point, the chills often stop.
Later, when the set point returns toward normal, the person may start:
Feeling hot
Sweating
Removing blankets
Feeling flushed
Sweating helps the body lose excess heat.
What Temperature Is Considered Fever?
For practical purposes, 38°C or higher is generally regarded as fever.
However, body temperature is not a fixed number.
It can vary depending on:
Time of day
Age
Physical activity
Environmental temperature
The site where temperature is measured
The type of thermometer used
This is why it is better to look at both the thermometer reading and the person's overall condition.
How Should You Measure Body Temperature?
Using a thermometer is much more reliable than touching someone's forehead.
A person's skin may feel hot or cold depending on room temperature, sweating and blood flow, so touch alone cannot accurately determine body temperature.
Digital thermometers are widely used for home temperature measurement.
Depending on age and the device, temperature may be measured from areas such as:
Armpit
Mouth
Ear
Forehead
The correct technique depends on the thermometer being used, so follow the manufacturer's instructions.
For babies and young children, extra care should be taken to use an age-appropriate method.
Useful home-health item — Digital Thermometer
A reliable digital thermometer is probably the single most useful product to keep at home for monitoring fever.
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Fever Is a Symptom, Not Usually a Disease
A fever tells you that something is happening inside the body, but it does not tell you what the diagnosis is.
Many different conditions can produce exactly the same temperature.
For example, a temperature of 39°C could occur with:
Influenza
Another respiratory viral infection
Pneumonia
Urinary tract infection
Dengue
Malaria
Typhoid fever
Other infections
Less commonly, fever can occur with inflammatory diseases, certain cancers and reactions to some medicines. Infections remain the most common cause of acute fever.
Therefore, the symptoms accompanying the fever are extremely important.
Common Causes of Fever
1. Viral infections
Viruses are among the most common causes of short-lasting fever.
Examples include infections affecting the:
Nose
Throat
Airways
Lungs
Gastrointestinal system
Possible accompanying symptoms include:
Runny nose
Nasal congestion
Sore throat
Cough
Headache
Muscle aches
Tiredness
Reduced appetite
Many respiratory and gastrointestinal infections are viral.
This is also why antibiotics should not automatically be taken whenever someone develops fever.
Antibiotics treat certain bacterial infections; they do not work against viral infections such as colds and influenza.
Fever With Cough, Cold or Nasal Congestion
Fever occurring with:
Cough
Runny nose
Sneezing
Sore throat
Nasal congestion
often suggests a respiratory infection.
Many respiratory infections are viral and resolve with supportive care, although pneumonia and other serious respiratory infections can also produce fever.
Seek medical assessment if the person develops symptoms such as:
Significant breathing difficulty
Chest pain
Bluish lips
Confusion
Severe weakness
Rapid deterioration
2. Bacterial Infections
Bacteria can also cause fever.
Common examples include:
Urinary tract infections
Pneumonia
Certain throat infections
Skin and soft-tissue infections
Some gastrointestinal infections
The symptoms depend on the location of infection.
For example:
Fever + burning while urinating
May suggest a urinary tract infection.
Fever + cough + breathing difficulty
May occur with pneumonia.
Fever + redness, swelling and pain of the skin
May occur with a bacterial skin infection.
Determining whether an infection is viral or bacterial sometimes requires examination and investigations.
Do not start antibiotics simply because the temperature is high.
3. Fever With Vomiting or Diarrhea
Gastroenteritis can cause:
Diarrhea
Abdominal cramps
Nausea
Vomiting
Sometimes fever
Viruses are a common cause, although bacteria, parasites and other causes are possible.
One of the most important complications to watch for is dehydration.
Signs of Dehydration
Possible signs include:
Increased thirst
Dry mouth
Reduced urination
Dark urine
Dizziness
Weakness
In young children, warning signs may also include:
Fewer wet nappies
Dry mouth
Lack of tears
Poor feeding
Unusual sleepiness
Dehydration becomes particularly important when fever is accompanied by repeated vomiting or diarrhea.
Hydration During Fever
People with fever may lose more fluid because of:
Sweating
Increased breathing
Reduced appetite
Reduced fluid intake
Vomiting
Diarrhea
Regular fluids are therefore important unless a doctor has specifically advised fluid restriction.
Water and other normal tolerated fluids are usually adequate for uncomplicated fever.
When significant fluid and electrolyte loss occurs through vomiting or diarrhea, oral rehydration solution (ORS) may be useful.
Useful when vomiting or diarrhea is present — ORS
ORS helps replace both fluid and electrolytes lost from the body.
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Keeping water easily available can also encourage frequent drinking.
Practical option — Reusable Water Bottle
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4. Mosquito-Borne Illnesses Can Also Cause Fever
Not every fever with body pain is simply a viral cold.
Certain mosquito-borne illnesses can produce significant fever.
Dengue
Dengue may cause:
High fever
Severe headache
Pain behind the eyes
Muscle and joint pain
Nausea
Vomiting
Rash
Most cases improve, but some people develop severe dengue. Warning symptoms such as persistent vomiting, significant abdominal pain, bleeding or marked lethargy require prompt medical assessment.
Importantly, serious deterioration in dengue can sometimes occur around the time the fever starts settling, so improvement in the temperature alone does not always mean the illness has resolved.
Malaria
Malaria is another important cause of fever in areas where transmission occurs.
Early symptoms commonly include:
Fever
Chills
Headache
Severe malaria can cause confusion, seizures, severe weakness and breathing difficulty.
Anyone with possible exposure and compatible symptoms should receive appropriate testing rather than simply treating the fever at home.
Typhoid Fever
Typhoid can cause:
Prolonged fever
Fatigue
Headache
Nausea
Abdominal discomfort
Constipation or diarrhea
Because these symptoms overlap with many other illnesses, laboratory testing may be required to establish the diagnosis.
5. Non-Infectious Causes of Fever
Although infections are the most common cause, fever is not always caused by germs.
Less common causes include:
Autoimmune and inflammatory disorders
Certain cancers
Reactions to some medications
Other inflammatory conditions
Persistent, recurrent or unexplained fever therefore deserves medical evaluation rather than repeated self-treatment.
What Symptoms Can Occur With Fever?
Fever may be accompanied by:
Chills
Shivering
Sweating
Headache
Muscle aches
Joint pains
Weakness
Fatigue
Reduced appetite
Increased thirst
Irritability
However, symptoms from the underlying disease are usually more useful than the fever itself.
Pay Attention to Symptom Combinations
Fever + cough
Possible respiratory infection.
Fever + cough + breathing difficulty
Requires assessment for more serious respiratory illness.
Fever + painful urination
Possible urinary infection.
Fever + vomiting or diarrhea
Possible gastrointestinal infection; watch carefully for dehydration.
Fever + severe headache + neck stiffness
Requires urgent medical assessment.
Fever + rash
Can occur with many illnesses. The significance depends on the type of rash and the person's overall condition.
Fever + severe abdominal pain
Needs medical evaluation, especially if persistent.
Fever + confusion or unusual sleepiness
Potential warning sign requiring urgent medical assessment.
What Is the Difference Between Fever and Hyperthermia?
These terms are sometimes mistakenly used as if they mean the same thing.
They are different.
Fever
During fever, the brain deliberately raises the body's temperature set point.
The body then works to achieve that higher temperature.
Hyperthermia
During hyperthermia, body temperature rises despite the body's temperature set point remaining normal.
This can occur when the body absorbs or produces more heat than it can lose.
Severe heat-related illness is therefore very different from ordinary infection-related fever and may require emergency treatment.
Should You Try to Bring Every Fever Down?
No.
One of the biggest misunderstandings about fever is that the temperature must always be brought immediately back to normal.
In children, NICE specifically recommends not using fever-reducing medicines solely for the purpose of lowering the thermometer reading. Treatment should instead focus on discomfort or distress.
The goal is usually to make the patient comfortable while monitoring the underlying illness.
Fever Medicines: Paracetamol and Ibuprofen
Paracetamol and ibuprofen are commonly used to relieve fever-associated discomfort when appropriate.
They may help with:
Headache
Muscle aches
General discomfort
Pain
However, they do not treat most underlying infections.
A fever may therefore return after the medicine wears off if the illness is still present.
Do Not Judge the Illness by Whether Paracetamol Works
A common misconception is:
"The fever came down after paracetamol, so the illness cannot be serious."
This is not reliable.
Both mild and serious illnesses may temporarily respond to an antipyretic.
The person's:
Breathing
Alertness
Hydration
Circulation
Associated symptoms
Overall appearance
remain important.
Fever Medicines in Children
Medication in children deserves additional care.
The dose of a liquid medicine may depend on factors such as:
Child's weight
Age
Drug concentration
Specific product being used
Never estimate a child's dose using an ordinary kitchen teaspoon.
A proper oral syringe or medicine-measuring device provides more accurate measurement.
Paracetamol or ibuprofen may be considered when a child with fever appears distressed or uncomfortable, rather than simply because the temperature is elevated.
Do not routinely give both together, and do not alternate them unless advised by an appropriate healthcare professional.
Fever in Babies and Young Children
Fever deserves particular attention in young infants.
Children often develop fever with viral illnesses, and many improve without complications. However, younger infants have a greater risk of serious bacterial infection.
Baby Younger Than 3 Months
A baby younger than 3 months with a temperature of 38°C or higher requires prompt medical assessment.
Do not simply give fever medicine and wait at home.
Babies Aged 3–6 Months
A temperature of 39°C or higher in a baby aged 3–6 months is an important reason to seek urgent medical advice, particularly when accompanied by other symptoms or if the baby looks unwell.
Look at the Child, Not Just the Thermometer
This is one of the most important points for parents.
A child with fever should be observed for:
Alertness
Eye contact
Response to parents
Feeding
Drinking
Urination
Breathing
Skin colour
Rash
Persistent vomiting
Excessive sleepiness
Unusual irritability
Clinical assessment systems such as NICE's fever guidance place considerable importance on appearance, breathing, circulation, hydration and behaviour when evaluating the risk of serious illness.
For families who frequently care for young children, some parents prefer a quick-reading thermometer for monitoring.
Febrile Seizures
Some young children can develop seizures associated with fever.
A febrile seizure can be frightening for parents, but it does not mean every child with a high temperature will have one.
Importantly, fever medicines such as paracetamol and ibuprofen may improve comfort but do not reliably prevent febrile seizures.
A child experiencing a first seizure or a prolonged seizure needs urgent medical assessment.
Rest During Fever
Rest is useful because illness often produces:
Fatigue
Muscle aches
Weakness
Reduced appetite
There is usually no need to force someone with an uncomplicated fever to remain completely immobile in bed, but strenuous exercise should be avoided while they are unwell.
Comfortable, breathable clothing is generally preferable to excessively heavy layers.
Should You Cover Someone With Several Blankets?
During chills, people often want several thick blankets.
A light covering for comfort is reasonable, but deliberately overheating someone is unnecessary.
Once the chills pass, excessive clothing or bedding may make the person uncomfortable.
Children with fever should not be over-dressed or over-wrapped.
Should You Sponge Someone With Cold Water?
Routine cold-water sponging is not recommended for treating fever in children.
Cooling the skin aggressively can cause discomfort and shivering.
The objective of fever care should be comfort and treatment of the underlying illness rather than forcing the body temperature down as rapidly as possible.
What Should Someone Eat During Fever?
There is no special food that cures fever.
Reduced appetite is common when someone is sick.
Do not force large meals if the person does not feel hungry.
Instead, offer normal nutritious foods that are easy for the person to tolerate, such as:
Rice-based meals
Soups
Fruits
Vegetables
Yogurt if tolerated
Other regular foods
Maintaining adequate fluid intake is particularly important.
Is a Pulse Oximeter Necessary for Fever?
No.
A pulse oximeter is not a fever detector.
It measures:
Blood oxygen saturation (SpO₂)
Pulse rate
For a healthy person with a simple fever and no respiratory symptoms, it is usually unnecessary to repeatedly check oxygen saturation.
However, it may be useful when someone has respiratory symptoms or when oxygen monitoring has been advised by a healthcare professional.
Most importantly, do not allow a seemingly acceptable device reading to override serious symptoms.
Someone struggling to breathe needs medical assessment regardless of what a home device displays.
Optional monitoring device — Fingertip Pulse Oximeter
Most relevant when respiratory symptoms are present or monitoring has been medically advised.
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Preventing the Spread of Infection at Home
Because many fevers are caused by infectious illnesses, simple hygiene practices can reduce transmission.
These include:
Washing hands regularly
Covering coughs and sneezes
Disposing of used tissues properly
Avoiding unnecessary sharing of drinking glasses and personal items
Cleaning frequently touched surfaces when appropriate
Practical hygiene item — Disposable Tissues
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When soap and water are not conveniently available, an appropriate hand sanitizer can also be useful.
Practical hygiene item — Hand Sanitizer
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When Should an Adult With Fever See a Doctor?
There is no single temperature number that answers this question for every adult.
Medical assessment should be considered when:
Fever is persistent or repeatedly returns
Symptoms are becoming worse rather than better
The cause is unclear
The person is significantly weak
There is persistent vomiting
Drinking is difficult
There are signs of dehydration
People with significant chronic disease or weakened immune systems may require earlier medical assessment.
Seek Urgent Medical Care When Fever Is Accompanied By:
Significant difficulty breathing
Severe chest pain
Confusion
Difficulty waking the person
Seizure
Severe headache with neck stiffness
Persistent vomiting
Severe dehydration
Blue or grey lips or skin
Significant unexplained bleeding
Rapid deterioration
A seriously unwell appearance
The underlying symptoms and clinical condition are often more important than the exact temperature reading.
When Should a Child With Fever Receive Urgent Medical Attention?
Seek urgent medical assessment if the child:
Is younger than 3 months with a temperature of 38°C or higher
Is 3–6 months with a temperature of 39°C or higher
Has significant breathing difficulty
Is extremely sleepy or difficult to wake
Does not respond normally
Develops a seizure
Shows signs of significant dehydration
Has repeated vomiting
Develops a concerning rash
Looks pale, blue, grey or mottled
Appears increasingly unwell
Parents should also seek medical advice whenever they are concerned about a young child's condition, even if the temperature itself does not appear extremely high.
How Is the Cause of Fever Diagnosed?
Not everyone with fever needs blood tests.
A healthcare professional first considers factors such as:
Age
Duration of fever
Travel history
Exposure to sick people
Associated symptoms
Medicines being used
Existing medical conditions
Physical examination findings
Depending on the suspected cause, investigations may include:
Complete blood count
Urine examination
Urine culture
Blood cultures
Tests for particular infections
Chest imaging
Other investigations
Tests should be selected according to the clinical situation rather than performing every available test for every fever.
Why You Should Not Self-Start Antibiotics for Fever
Fever does not tell you whether an infection is bacterial.
Many common infections are caused by viruses.
Antibiotics:
Do not kill viruses
Do not shorten viral infections
Can produce side effects
Can contribute to antimicrobial resistance when used unnecessarily
If an antibiotic is actually required, the correct drug depends on the suspected organism, infection site, patient characteristics and local resistance patterns.
Common Fever Myths
Myth 1: Every fever is dangerous
Not true.
Fever is frequently part of the normal immune response to infection.
Myth 2: Higher temperature always means more serious disease
Not necessarily.
A relatively mild fever can occur with a serious illness, while a high fever may occur during a self-limiting viral infection.
Always consider the person's overall condition.
Myth 3: Every fever requires antibiotics
False.
Antibiotics do not treat viruses.
Myth 4: Fever medicine cures the infection
False.
Paracetamol and ibuprofen primarily relieve discomfort and reduce temperature. They do not cure most infections responsible for fever.
Myth 5: If the fever comes down after medicine, the illness is definitely harmless
False.
Response to fever medicine cannot reliably distinguish serious illness from a minor illness.
Myth 6: Cold-water baths are the best way to control fever
No.
Aggressive cooling can cause discomfort and shivering, particularly in children.
Myth 7: You should stop drinking water when you have fever
Definitely not.
Adequate fluid intake is an important part of uncomplicated fever care unless a healthcare professional has specifically restricted fluids.
A Simple Approach to Fever at Home
For an otherwise healthy person with a mild illness and no warning signs:
1. Measure the temperature
Use a reliable thermometer.
2. Look for other symptoms
Do not focus only on the temperature.
Check for:
Cough
Breathing difficulty
Rash
Vomiting
Diarrhea
Urinary symptoms
Headache
Abdominal pain
3. Maintain hydration
Encourage regular fluids.
4. Rest
Avoid unnecessary strenuous activity while unwell.
5. Use fever medicine only when appropriate
The purpose is usually to improve comfort, not simply achieve a normal thermometer reading.
6. Monitor the trend
Ask whether the patient is:
Improving
Staying the same
Becoming worse
7. Watch for warning signs
Seek medical help when concerning symptoms develop.
Useful Items for a Basic Fever-Care Kit
You do not need a large collection of products simply because someone develops fever.
A small, sensible home health kit is usually enough.
The products mentioned throughout this article are:
Digital thermometer
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Amazon USAORS — particularly useful when vomiting, diarrhea or dehydration occurs
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Amazon USAReusable water bottle
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Amazon USAPulse oximeter — mainly relevant when respiratory symptoms or medical indications are present
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Amazon USADisposable tissues
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Amazon USAHand sanitizer
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Amazon USAFirst-aid/medicine storage organizer
A convenient way to safely keep thermometers, ORS, medicine-measuring devices and other basic health supplies together and away from children.
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These products are supportive tools, not treatments for the underlying cause of fever. Most people do not need to purchase all ten.
Frequently Asked Questions About Fever
Is 37°C a fever?
Usually no. Normal body temperature varies between individuals and during the day.
Is 38°C a fever?
Yes. A temperature of 38°C or higher is generally considered fever.
Is 39°C dangerous?
The temperature should not be interpreted in isolation.
Consider:
Age
Alertness
Breathing
Hydration
Associated symptoms
Duration of illness
In babies aged 3–6 months, 39°C or higher is an important reason to seek medical advice.
Can fever cause dehydration?
Yes. Fever can contribute to increased fluid loss, and the risk becomes greater if vomiting or diarrhea is also present.
Should I take antibiotics if my fever lasts two days?
Not automatically.
The duration of fever alone cannot determine whether an antibiotic is required.
Should I eat normally during fever?
You can generally eat according to appetite and tolerance. There is no special universal fever diet.
Can I take a bath during fever?
Normal personal hygiene can continue if the person feels well enough. Avoid using extremely cold water specifically to force the temperature down.
Is sweating a sign that fever is reducing?
Sweating often occurs when the body's temperature set point begins returning toward normal, but it should not be used as the only indication that an illness is improving.
The Most Important Message About Fever
Treat the patient, not just the thermometer.
When someone has fever, ask:
Are they alert?
Are they breathing comfortably?
Are they drinking?
Are they passing urine?
Are they able to communicate normally?
Are their symptoms improving?
Are any warning signs developing?
These questions often provide much more useful information than repeatedly checking whether the temperature is 38.5°C or 39°C.
Final Thoughts
Fever is not usually an illness by itself. It is a physiological response that most commonly occurs when the immune system is reacting to an infection.
For uncomplicated fever, basic measures such as proper temperature measurement, adequate fluids, rest and appropriate symptom relief are often sufficient while the illness runs its course.
At the same time, fever should never be dismissed when it occurs in a very young infant or when it is accompanied by breathing difficulty, confusion, severe dehydration, seizures, persistent vomiting, concerning rash, severe pain or rapid worsening.
Knowing when home care is reasonable and when medical evaluation is necessary is far more important than simply trying to make the thermometer display 37°C.
Evidence Sources
This article was prepared using guidance and medical information from:
NHS — High temperature (fever) in adults
NHS — High temperature (fever) in children
NICE — Fever in under 5s: assessment and initial management
American Academy of Pediatrics / HealthyChildren.org — Fever guidance for parents
WHO — Dengue, malaria and typhoid guidance
CDC — Appropriate antibiotic use
NIH/NCBI — Physiology of fever
Medical Disclaimer
This article is intended for general health education and should not be used as a substitute for individualized medical diagnosis or treatment. Seek evaluation from a qualified healthcare professional when fever is persistent, worsening, occurs in a very young infant, or is accompanied by concerning symptoms.
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