Also known as: Pyrexia
A fever is a temporary rise in body temperature, typically above 100.4 degrees F (38 degrees C), and is one of the body's natural defenses against infection. Fevers are extremely common and are usually a sign that the immune system is actively fighting off an illness. Most fevers resolve on their own within a few days.
A fever is one of the body's most ancient and effective defense mechanisms against infection. When the immune system detects invading bacteria, viruses, or other pathogens, it releases chemicals called pyrogens that raise the body's thermostat in the hypothalamus. The higher temperature makes the body a less hospitable environment for pathogens and also helps immune cells work more efficiently.
Normal body temperature varies from person to person and throughout the day, ranging from about 97°F to 99°F (36.1°C to 37.2°C). A temperature of 100.4°F (38°C) or higher is generally considered a fever. Low-grade fevers (100.4-102°F) are common with many viral illnesses and often do not require treatment beyond rest and fluids.
While fever itself is not an illness but a symptom, it can cause discomfort including chills, sweating, headache, muscle aches, and fatigue. In most healthy adults and older children, fever is not dangerous and resolves as the underlying infection clears. However, very high fevers, prolonged fevers, and fevers in vulnerable populations like infants and immunocompromised individuals require prompt medical attention.
There are several possible reasons you may be experiencing Fever. Here are the most common ones.
The commonest cause of fever. Colds, flu, and COVID-19 trigger a temperature as the immune system responds, usually with a runny nose, cough, sore throat, or aches. Most settle on their own within a few days.
Infections of the chest (pneumonia), throat (tonsillitis), skin (cellulitis), or other sites can drive a higher, more persistent fever and may need antibiotics. A fever that is climbing or not improving after a few days should be assessed.
A common and easily missed cause of fever, especially in women and older adults. It may come with burning on passing urine, needing to go often, or tummy or back pain, and in older people can show mainly as fever and confusion.
Stomach bugs from viruses or bacteria cause fever alongside diarrhoea, vomiting, and cramps. The main risk is dehydration, so keeping up fluids matters as much as the temperature itself.
A high body temperature from hot weather or heavy exertion is overheating rather than a true infection fever. Heatstroke, with confusion and a very high temperature, is a medical emergency and needs immediate cooling and help.
A mild, short-lived fever is a normal immune response after some vaccinations. Certain medications can also cause fever as a side effect, which settles once the cause is identified.
After travel to affected regions, infections such as malaria and dengue are important causes of fever and can be serious. Any fever within a few weeks of travelling to a malaria area needs prompt medical assessment.
Autoimmune and inflammatory conditions can cause recurring fevers without an infection. When a fever persists and standard tests are normal, doctors investigate for a hidden cause, an approach known as a fever of unknown origin workup.
These approaches may help manage fever at home. Always consult a healthcare provider if symptoms persist or worsen.
The body needs extra energy and fluids to fight infection. Drink plenty of water, clear broths, and electrolyte solutions to replace fluids lost through sweating. Rest allows the immune system to focus on fighting the underlying cause.
A lukewarm (not cold) sponge bath or placing a cool, damp cloth on the forehead can help bring down body temperature gradually. Avoid cold baths or ice, which can cause shivering that actually raises core temperature.
Wear lightweight, breathable clothing and use light bedding to allow heat to dissipate from the body. Remove extra layers of blankets even if you feel chilly — bundling up traps heat and can raise temperature further.
Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) can help reduce fever and relieve associated discomfort. Follow dosage instructions carefully and avoid giving aspirin to children or teenagers due to the risk of Reye's syndrome.
Keep the room at a comfortable temperature (around 68-72°F). Use a fan for air circulation if helpful. A cool, well-ventilated room supports the body's natural cooling mechanisms.
Doctors evaluate fever by measuring body temperature and performing a thorough physical examination to identify the source of infection or inflammation. They will examine the ears, throat, lungs, abdomen, skin, and lymph nodes. Blood tests including a complete blood count (CBC), C-reactive protein (CRP), and blood cultures can help distinguish between viral and bacterial infections. Urine analysis and chest X-rays are common when the source is not immediately apparent. In cases of prolonged unexplained fever, additional testing may include autoimmune markers, CT scans, or other specialized studies.
Seek urgent medical help for a fever with a stiff neck, a rash that does not fade under pressure, severe headache, sensitivity to light, or new confusion or drowsiness, as these can signal meningitis or sepsis. Get help for a very high temperature above 103 degrees F (39.4 degrees C) that will not come down, a fever with breathing difficulty, chest or severe abdominal pain, or signs of sepsis such as fast breathing, mottled skin, or passing little urine. See a doctor for a fever lasting more than three to five days or one that keeps returning, and for any fever after travel to a malaria area. A baby under three months with any fever should be seen the same day.
Steps you can take to reduce the likelihood of experiencing fever.
Wash hands frequently with soap and water and avoid touching your face
Stay up to date on recommended vaccinations, including flu and COVID-19
Avoid close contact with people who are visibly ill
Practice good food safety and hygiene to prevent foodborne infections
Support your immune system through adequate sleep, regular exercise, and balanced nutrition
A body temperature of 100.4 degrees F (38 degrees C) or higher is generally considered a fever. Normal temperature varies from person to person and through the day, roughly 97 to 99 degrees F (36.1 to 37.2 degrees C). A low-grade fever is around 100.4 to 102 degrees F and is common with everyday viral illnesses.
As well as a raised temperature, a fever often brings chills or shivering, sweating, headache, muscle aches, tiredness, and sometimes a flushed face and reduced appetite. These come from the body raising its thermostat to fight infection, and they usually ease as the temperature settles.
A fever needs urgent attention if it comes with a stiff neck, a rash that does not fade under pressure, severe headache, light sensitivity, confusion, breathing difficulty, or signs of sepsis such as fast breathing and little urine. A very high temperature that will not come down, a fever lasting more than three to five days, or a fever after travel to a malaria area also need medical review.
Most fevers are caused by infection, usually viral (colds, flu, COVID-19) and sometimes bacterial (chest, throat, urine, or skin). Other causes include stomach bugs, overheating from hot weather, a normal response after vaccination, some medications, tropical infections such as malaria and dengue after travel, and, less often, inflammatory conditions.
Rest, drink plenty of fluids, and keep to light clothing and a cool room. Paracetamol or ibuprofen can ease the discomfort of a fever if you need it and it is safe for you. There is no need to force the temperature down if you are otherwise coping, but do seek help if warning signs appear or the fever will not settle.
Most fevers from everyday infections settle within three to five days as the illness clears. See a doctor if a fever lasts longer than this, keeps coming back, climbs very high, or comes with any of the warning signs above. Trust your judgement: a fever with someone who looks or feels very unwell always deserves assessment.
Yes. Overheating in hot weather, a reaction to a vaccination or medication, and inflammatory or autoimmune conditions can all raise the temperature without an infection. Persistent fevers with no obvious infectious cause are investigated by doctors as a fever of unknown origin.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.