Fever

Normal body temperature is around 37°C (98.6°F), although this varies from person to person and changes slightly over the course of the day and night. A fever is a temperature that rises above this normal range, usually because the immune system has reset the body’s internal thermostat to a higher level in response to infection.

Contrary to popular belief, how high a fever climbs is not a reliable measure of how serious the underlying illness is. A life-threatening condition may produce only a small rise in temperature, while a minor infection can cause a higher one. Most cases of mild fever settle on their own within a couple of days, and a mild fever (up to about 39°C (102.2°F)) can actually help the immune system clear an infection.

In children between the ages of 6 months and 6 years, a fever can sometimes trigger a convulsion. A very high fever of 42.4°C (108.3°F) or above, particularly in older people, can damage the brain.

Symptoms of fever#

The symptoms of a fever can include:

• a flushed face
• feeling generally unwell
• feeling hot and sweaty
• shivering or shaking
• chattering teeth

What causes fever#

Infection is usually the cause of a fever. This can include:

• illnesses caused by viruses, such as colds, flu, COVID-19 and other upper respiratory tract infections
• illnesses caused by bacteria, such as tonsillitis, pneumonia or urinary tract infections
• some chronic illnesses, such as rheumatoid arthritis and ulcerative colitis, which can cause fevers that last longer
• some tropical diseases, such as malaria (which can cause recurring bouts of fever) or typhoid
• heat stroke, which can include fever without sweating as one of its symptoms
• certain medicines, which can cause fever as a side effect in some people

Looking after yourself with a fever#

If you have a fever, some simple steps can help you feel more comfortable and bring your temperature down:

• Take paracetamol (acetaminophen) or ibuprofen in the appropriate dose to help lower your temperature.
• Drink plenty of fluids, particularly water, and avoid alcohol.
• Sponge exposed skin with tepid (lukewarm) water. Standing in front of a fan can boost the cooling effect of evaporation.
• Make sure you get plenty of rest, including bed rest.

Avoid cold baths or showers. The skin reacts to cold by tightening its blood vessels, which traps body heat, and the cold can also cause shivering, which generates more heat.

When to see a doctor#

Consult your doctor if:

• you are still feverish after 3 days, despite home treatment
• your temperature is over 40°C (104°F)
• you are shivering and shaking involuntarily, or your teeth are chattering
• you seem to be getting sicker as time goes on
• you have a severe headache
• you have recently travelled overseas
• you have unusual symptoms such as hallucinations, vomiting, neck stiffness, a skin rash, a rapid heart rate, chills or muscle spasms

Seek urgent medical attention#

Seek immediate medical help if you or someone else has:

• a fever with a severe headache and a stiff neck
• a rash that does not fade when you press on the skin, which suggests bleeding under the skin and can be a sign of a life-threatening illness
• confusion and drowsiness

How fever is diagnosed and treated#

Because a fever is a symptom rather than an illness in itself, the underlying cause must be found before specific treatment can begin. After taking a medical history and examining you, your doctor may order tests if the cause is not clear. These can include:

• blood tests
• urine examination and culture
• throat swabs or a mucus sample for examination and culture
• stool examination and culture
• x-rays

Treatment depends on the cause. For example, chronic tonsillitis may need surgery to remove the tonsils (tonsillectomy). Fevers caused by viral illnesses should not be treated with antibiotics, because these drugs have no effect against viruses. Even with a mild bacterial infection, it is often best to let your immune system handle the problem rather than take antibiotics.

Fever in children#

On average, a young child has up to 10 infections a year. Body temperature is not a reliable indicator of how ill a baby or young child is. A child can have a mild temperature on the thermometer (slightly over 37°C (98.6°F)) yet still seem happy and well, while another child may seem unwell with only a small rise.

See a doctor straight away if your child:

• is aged 6 months or less
• has a rash
• has a fever of 40°C (104°F) or more
• is still feverish after a day or so, despite regular doses of children’s paracetamol
• vomits or has persistent diarrhoea
• refuses food or drink
• cries inconsolably or is in pain
• seems listless, floppy or just looks ill
• has a convulsion or twitching
• has trouble breathing

If you are worried or concerned at any stage, consult your doctor.

Using a thermometer#

If you think your child has a fever, you can use a thermometer to measure their temperature. Remember that the reading is best used as a guide rather than a definite sign of illness. Several types of reliable thermometer are available, each with instructions on how to use it. If you are unsure which one to choose, or have questions about how to use it, ask your pharmacist to explain.

Caring for a child with a fever#

• Dress your child in light clothing and keep them cool.
• Give drinks of clear fluid, such as water.
• Give paracetamol in the correct dose for the child’s age, but not more than 4 doses in any 24-hour period. Do not give regular paracetamol for more than 24 hours without seeking advice from your doctor.
• Do not give your child a cold bath.
• See your doctor if your child is 3 months or younger.

Febrile convulsions#

A febrile convulsion is a fit or seizure that occurs in babies and children when they have a high fever, often from an ear infection or a viral upper respiratory infection. The fit can last from a few seconds up to about 15 minutes and is followed by drowsiness. Approximately 3% of otherwise healthy children will have one or more febrile convulsions between the ages of 6 months and 6 years. There is no way to predict who will be affected or when. A febrile convulsion does not cause brain damage.

Symptoms of a febrile convulsion can include:

• loss of consciousness (blacking out); a standing child will fall and may pass urine
• twitching or jerking of the arms and legs
• breathing difficulty
• foaming at the mouth
• going pale or bluish in skin colour
• eye rolling, so only the whites of the eyes are visible
• taking up to 15 minutes to wake up properly afterwards, during which the child may be irritable and appear not to recognise you

What to do during a convulsion#

Convulsions are frightening to watch but are rarely serious. If your child has a convulsion, you should:

• Try to stay calm and don’t panic.
• Place your child on the floor and remove any objects they could knock against.
• Don’t force anything into your child’s mouth.
• Don’t shake, slap or try to restrain your child.
• Once the convulsion has stopped, roll your child onto their side into the recovery position.
• If there is food in their mouth, turn their head to the side and do not try to remove it.
• Note the time the fit started and stopped, so you can tell the doctor.

Have your child checked by a doctor or the nearest hospital emergency department as soon as possible after the fit stops, to find the cause of the fever. Call your local emergency number (for example 911 in the US and Canada, 112 across the EU and many countries, 999 in the UK, or 000 in Australia) for an ambulance if the fit lasts more than 5 minutes.

Key points#

• Fever is a rise in body temperature above normal, usually caused by infection.
• The height of a fever is not a reliable guide to how serious the illness is.
• Drink plenty of fluids and use paracetamol or ibuprofen to feel more comfortable.
• Fevers caused by viral illnesses should not be treated with antibiotics.
• Because fever is a symptom and not an illness, the underlying cause must be found before specific treatment can begin.
• A febrile convulsion can occur in young children with a high fever and, although alarming, does not cause brain damage.

Where to get help and trusted information#

For evidence-based global health guidance, see Source: World Health Organization (WHO).