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.
Viruses are the most common cause of fever, including those responsible for colds, flu, COVID-19, and many childhood illnesses. Viral fevers typically resolve within 3-5 days as the immune system fights off the infection.
Bacterial infections such as urinary tract infections, strep throat, pneumonia, and skin infections often cause fever, sometimes higher than viral infections. Bacterial fevers may require antibiotic treatment.
Autoimmune diseases like rheumatoid arthritis, lupus, and inflammatory bowel disease can cause low-grade fevers during flare-ups. The inflammation triggers the same immune response as an infection, raising body temperature.
Some medications, including certain antibiotics, seizure medications, and blood pressure drugs, can cause drug fever as a side effect. This type of fever typically resolves once the medication is stopped.
Prolonged exposure to high temperatures or intense physical activity in hot conditions can overwhelm the body's cooling mechanisms. Unlike infection-related fevers, heat illness requires external cooling measures.
A low-grade fever after vaccination is a normal immune response indicating that the body is building protection against the targeted disease. These fevers are typically mild, lasting 1-2 days.
Teething may cause a slight increase in temperature in babies but does not cause true high fevers. If an infant has a fever above 100.4°F, another cause should be investigated regardless of teething status.
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 medical attention if a fever exceeds 103 degrees F (39.4 degrees C), lasts more than three days, or is accompanied by severe headache, stiff neck, confusion, persistent vomiting, or a rash. Infants under three months with any fever should be seen immediately.
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
For most healthy adults and older children, a low-grade fever does not necessarily need to be treated with medication. Fever helps the immune system fight infections more effectively. However, treating fever is reasonable if it causes significant discomfort, interferes with sleep, or reaches higher levels. The goal of treatment is comfort, not necessarily returning temperature to normal.
In healthy adults, a fever above 103°F (39.4°C) warrants medical attention, as does any fever lasting more than 3 days. In infants under 3 months, any fever of 100.4°F or higher is an emergency. For children 3 months to 3 years, fevers above 102°F should be evaluated, and any fever with concerning symptoms like lethargy, rash, or stiff neck needs immediate attention.
Yes, fevers can occur without an infection. Autoimmune conditions, inflammatory diseases, certain cancers, medication reactions, and heat-related illness can all cause elevated body temperature. If you have a persistent or recurrent fever without obvious infection symptoms, it is worth discussing with your doctor to investigate other potential causes.
Rectal thermometers are considered the most accurate, especially for infants. Oral thermometers are reliable for older children and adults when used correctly. Temporal (forehead) and tympanic (ear) thermometers are convenient and reasonably accurate for screening. Axillary (armpit) temperatures tend to read about 1°F lower than core temperature. For consistency, use the same type and method each time you check.
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.