What is a Fever?

A fever is a temporary increase in your body temperature, often due to an illness. Having a fever is a sign that something out of the ordinary is going on in your body.

Technically, any body temperature above the normal oral measurement of 98.6 Fahrenheit (37 Celsius) or the normal rectal temperature of 99 F (37.2 C) is considered elevated. However, one’s normal body temperature may actually be 1 F (0.6 C) or more above or below the average of 98.6 F. Body temperature can also vary up to 1 F (0.6 C) throughout the day. A fever is not considered medically significant until body temperature is above 100.4 F (38 C). Anything above normal but below 100.4 F (38 C) is considered a low-grade fever.

Fever serves as one of the body’s natural defenses against bacteria and viruses. For that reason, low-grade fevers may normally go untreated, unless accompanied by troubling symptoms or signs. Fevers of 104 F (40 C) or higher may be dangerous and demand immediate attention, as they can result in delirium and convulsions, particularly in infants, children, and the elderly.


Symptoms of Fever

You have a fever when you have an elevated body temperature.

Depending on what’s causing your fever, additional fever signs and symptoms may include sweating, shivering, headache, muscle aches, loss of appetite, dehydration, and general weakness.

High fevers between 103 F (39.4 C) and 106 F (41.1 C) may cause hallucinations, confusion, irritability, convulsions, and dehydration.


Causes of Fever

Fever is the result of an immune response by your body to a foreign invader. Foreign invaders include viruses, bacteria, fungi, drugs, or other toxins.

Although the most common causes of fever are common infections such as colds and viruses, other causes include:

  • Infections of the ear, lung, skin, throat, bladder, or kidney
  • Side effects of drugs
  • Cancer
  • Vaccines
  • Blood clots
  • Autoimmune diseases such as lupus, rheumatoid arthritis, and inflammatory bowel disease
  • Hormone disorders such as hyperthyroidism
  • Heat exhaustion
  • Extreme sunburn
  • Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints
  • Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
  • Some immunizations and vaccines

Treatments for Fever

The most common treatments for fever include over-the-counter drugs such as acetaminophen (Tylenol) and non-steroidal anti-inflammatory drugs such ibuprofen (Advil, Motrin) and naproxen (Aleve). Children and teens should not take aspirin because it’s linked to condition called Reye’s syndrome.

An individual with a fever should be kept comfortable and not overdressed. Overdressing can cause the temperature to rise further. Tepid water (85 F [30 C]) baths are a home remedy that may help bring down a fever. Never immerse a person with a fever in ice water. This is a common misconception. Drink plenty of water, and avoid alcohol or caffeinated beverages, which can contribute to dehydration.

Depending on the cause of your fever, your doctor may prescribe an antibiotic, especially if he or she suspects a bacterial infection, such as pneumonia or strep throat.

For infants, especially those younger than 28 days, your baby might need to be admitted to the hospital for testing and treatment. In babies this young, a fever could indicate a serious infection that requires intravenous (IV) medications and round-the-clock monitoring.