Fever

A fever is a temporary rise in body temperature, often because the immune system is responding to an infection. It is a symptom rather than a disease.

A temperature of 38°C (100.4°F) or higher is commonly considered a fever. Readings vary depending on whether the temperature is taken in the mouth, ear, armpit, or rectum. Record both the reading and where it was taken.

Feeling someone’s forehead cannot confirm a fever. Use a digital thermometer and follow its instructions.

The height of a fever does not always show how serious the cause is. Age, medical history, other symptoms, and how alert and comfortable the person appears are also important.

You may feel hot, cold, or both at different times. Chills can occur as the temperature rises, even when the skin feels warm.

Other possible symptoms include:

• Sweating, shivering, or flushed skin
• Tiredness, weakness, muscle aches, or headache
• Reduced appetite or thirst
• Faster heartbeat or breathing
• Signs of mild dehydration

Children may be irritable, sleepy, less active, or feed less. A child who interacts, drinks, and responds normally is generally less concerning than one who is difficult to wake or unusually unresponsive.

Older adults and people with weakened immune systems can have a serious infection without a high temperature. New changes in alertness, breathing, or general condition are important even without a clear fever.

Common causes include viral infections such as colds, influenza, COVID-19, and stomach infections. Bacterial causes include urinary tract infections, strep throat, skin infections, and some chest infections.

A mild, short-lived fever can follow vaccination. Follow the vaccine information and seek advice if symptoms are stronger or last longer than expected.

Less common causes include inflammatory conditions and reactions to certain medicines. Rarely, persistent fever may be associated with a blood disorder or cancer.

Urgent causes include meningitis, sepsis, and heatstroke. These usually cause other serious symptoms in addition to fever.

Call emergency services if fever occurs with:

• Severe trouble breathing, blue or grey skin, or collapse
• New confusion, extreme difficulty waking, or loss of consciousness
• A seizure, especially a first seizure or one that is continuing
• A stiff neck with severe headache or marked sensitivity to light
• A rash that does not fade when pressed with a clear glass
• Very hot skin after heat exposure, especially with confusion

Seek urgent, same-day medical advice for a baby younger than 3 months with a rectal temperature of 38°C (100.4°F) or higher.

Get same-day advice if you have a weakened immune system, are receiving chemotherapy, recently had major surgery, or have a fever plan from your care team. Follow that plan if it uses a lower threshold.

Contact a healthcare professional promptly for signs of dehydration, including very little urine, a very dry mouth, no tears, or inability to keep fluids down.

Book a routine appointment if the fever lasts more than about three days, keeps returning, worsens after initial improvement, or occurs with unexplained weight loss, night sweats, persistent pain, or another concerning symptom. Children younger than 6 months may need earlier assessment.

A healthcare professional may ask when the fever began, how it was measured, and which other symptoms are present. Recent travel, exposure to illness, insect bites, vaccinations, new medicines, and existing conditions may provide clues.

The examination may focus on the ears, throat, chest, abdomen, skin, joints, or nervous system.

Many short-lived fevers need no tests. If testing is needed, it may include a nose or throat swab, urine or blood test, or chest X-ray. Young babies, people with weakened immune systems, and those who appear very unwell may need urgent or more detailed testing.

Treatment depends on the cause. Viral infections often improve without specific treatment. Antibiotics like amoxicillin or doxycycline may treat bacterial infections but do not work against viruses.

Rest and drink enough fluid to keep urine pale yellow. Try small, frequent drinks if you feel sick. Wear light clothing and keep the room comfortable. Avoid ice baths, cold-water sponging, and alcohol rubs because they may cause shivering or harm.

Paracetamol, also called acetaminophen, or ibuprofen may reduce discomfort. Use only a product suitable for the person’s age and follow the label or professional advice. Do not give aspirin to children or teenagers because of the risk of Reye syndrome. Ask for advice before giving fever medicine to a young baby.

The goal is comfort and hydration, not forcing the temperature to normal. Fever medicine may lower it temporarily without treating the cause.

A fever caused by a routine viral infection often improves within a few days. The temperature may rise and fall during recovery.

Monitor alertness, breathing, fluid intake, urination, and whether other symptoms are improving. Arrange follow-up if the fever continues beyond the expected course, returns after being absent, or new symptoms develop. Seek care sooner if the person’s general condition worsens, even if the temperature is not especially high.

Can teething cause a fever?

Teething may cause mild discomfort and a small temperature increase. Do not automatically blame a temperature of 38°C or higher on teething, especially if the baby seems unwell.

Is fever itself dangerous?

Most infection-related fevers are not harmful by themselves. The cause and accompanying symptoms matter more than the number alone. Very high body temperature from heatstroke is different and requires emergency care.

Can fever cause seizures in children?

Some children between about 6 months and 5 years can have a febrile seizure. These are usually brief. Call emergency services for a first seizure, one that continues, breathing difficulty, or poor recovery afterward.

Can I tell whether an infection is viral or bacterial from the temperature?

No. Both can cause mild or high fever. Diagnosis depends on the overall symptoms, examination, and sometimes tests.