A body temperature of more than 37.2°C or 98.9°F in the morning or a temperature of more than 37.7° or 99.9°F in the evening indicates fever.

Fever is a symptom that has plagued each of us at some time or the other. Often, people try to treat fever at home. A better understanding about fever will no doubt help in managing fever better at home; it will also ensure that a doctor is consulted at the right time.


Man is a warm-blooded animal, that is, body temperature is maintained regardless of the environmental temperature. The normal temperature of the body is maintained at 37°C or 98.6°F by the hypothalamus, a small but important part situated just below the brain. A slight variation of 0.5°C or 0.9°F occurs during the day.

Fever is defined as a before-noon temperature of more than 37.2°C or 98.9°F or an afternoon temperature of more than 37.7°C or 99.9°F. Fever is an elevation in normal body temperature that occurs in connection with a raised hypothalamic set point.

Body temperature is measured using a thermometer. The reading is obtained either by placing a thermometer in the mouth, in the rectum (especially in children), from the ear near the ear drum or in the armpit. Rectal temperatures are usually 0.5°C or 0.7°F higher than oral temperatures. Temperatures taken in the armpit are usually not very reliable.

Very high temperature of more than 41.5°C or 106.7°F is called hyperpyrexia. It occurs due to brain hemorrhage or severe infections.


Some causes of fever are listed below:

  • Infections: Viral, bacterial, fungal or protozoal infections often cause fever. Some additional features that can help in the diagnosis of fever due to infections are:
  • Fever of short duration without specific symptoms may be due to influenza
  • Fever with throat pain and difficulty in swallowing could be due to sore throat infection, diphtheria or infectious mononucleosis (infection by a virus called Epstein-Barr virus)
  • Fever with cough, chest pain and rusty sputum may be due to pneumonia
  • Fever with rigors and burning while passing urine indicates a urinary tract infection
  • An alternate day fever with rigors indicates malarial infection
  • Fever with swelling of feet with rigors and a raised eosinophil count may indicate filariasis
  • An increasing fever with pain in abdomen, small red spots on the skin and a slow heart rate could be due to typhoid
  • Fever with neck stiffness, headache and vomiting may be due to meningeal infection (infection of the covering of the brain)
  • Fever with cough over a long duration and weight loss may indicate tuberculosis
  • Fever with rashes may be due to a viral infection
  • Short-duration fever with progressive weight loss and a high-risk behavior could possibly be due to HIV infection
  • Drugs and Biological Agents: Drugs like beta-lactam antibiotics, procainamide, isoniazid, alpha-methyldopa, quinidine and diphenylhydantoin are associated with fever. Biological agents like interferons and interleukins used in therapy could also cause fever. Vaccines could also result a temporary rise in temperature. Fever caused by drugs is often associated with a rash.
  • Tissue injury: Heart attack, burns, trauma and injections into muscles damage tissues and can cause fever.
  • Cancers: Blood cancers like leukemia and lymphoma, and liver cancer can cause fever. The liver, spleen and lymph nodes may be enlarged and easily felt in these conditions.
  • Inflammatory diseases: Rheumatoid arthritis, systemic lupus erythematosus and inflammatory bowel disease are some inflammatory diseases that could cause a rise in body temperature.
  • Hormonal diseases: Thyrotoxicosis (a condition in which the thyroid gland is hyperactive) and pheochromocytoma (a condition in which the adrenal gland is affected) can cause fever.
  • Metabolic diseases: Gout and increase in blood urea can sometimes raise the body temperature.
  • Genetic diseases: Familial Mediterranean fever is a genetic disease with fever as one of its symptoms.

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